As costume disasters go, what two National Ballet of Canada dancers suffered in “The Merry Widow” some years ago was extreme. At one point in Act 2, the French attaché’s jacket buttons caught on his lover’s gown, and as he spun her in his arms she began to lose her dress.

Torn silk entangled them. The more the young man tried to free himself, the worse it got. The audience was in fits of laughter. The whole evening was unraveling along with the ballerina’s costume, replaced by a screwball comedy. One man kept it together: conductor Ormsby Wilkins.

Down in the orchestra pit, Wilkins tuned out the uproar and calmly sustained a romantic musical mood. He tossed a metaphoric lifeline to the dancers, unspooling the Franz Lehár score with warmth and a consistent tempo.

“Naturally, the band played on,” Wilkins recalls. “You just keep going. The ballerina ended up with less of the dress at the end of the pas de deux than she had at the beginning. But eventually her partner got rid of all the extra that came off, and they found their way back to the music.”

The scene ended with the noisiest ovation the conductor had ever heard. Surely some part of that was due to the musical continuity. Wilkins, who became American Ballet Theatre’s music director in 2005, is too modest to say this, so I shall: Ballet conductors are the hidden heroes of the art form. They can serve as guardian angels of the evening, controlling the musical universe and its atmosphere, smoothing over mishaps and delivering well-timed thunderbolts with a wave of the baton. They can even see the future, reading signs of trouble in a dancer’s hesitancy or hint of fatigue, and adjusting the tempo for what comes next.

These conductors’ names are seldom known to even the most ardent dance fans, and they’ll never attain the public persona of a Gustavo Dudamel or a Valery Gergiev (both of whom, incidentally, have occasionally conducted for dance). Yet despite quieter profiles, ballet conductors arguably do twice the work of their symphonic counterparts.

Ballet conductors have two armies to marshal: the orchestra and the dancers. The best are fluent in the differing languages of music and dance. They have to digest the ballet repertoire, and be able to grasp the intent of the characters and scenes. They need to understand dancer priorities (consistency, above all), and where the performers are likely to tire or get nervous, and how a slower or peppier pace can magic away the evidence.

These conductors also must diplomatically negotiate, with each leading performer, the musical interpretation of, say, every solo in “Swan Lake,” and then repeat the bargaining in rehearsals with the different casts scheduled throughout the company’s performances. Each dancer moves at a different natural rhythm, and has different strengths to display. If they’re lucky enough to perform with live music, dancers know that whoever holds the baton is crucial to their success.

“The dancer’s fate is in the hands of the conductor,” says Skylar Brandt, a soloist with American Ballet Theatre. “The conductor is as much a partner to the dancer as your dance partner.”

Unfortunately for Brandt, and Wilkins, and the rest of the world’s ballet ecosystem, audiences won’t witness this harmony between conductor and ballet cast any time soon. Not in a live performance, anyway, with the covid-19 pandemic forcing cancellations at least through the summer. But if you’re inclined to watch a major ballet company on video, DVD or a streaming service, chances are that a conductor and orchestra will be part of the experience. (Performances are also being offered online by various companies and venues; for instance, New York City Ballet is offering a digital spring season, streaming two ballets a week.)

Maria Seletskaja, conductor-in-residence at the National Ballet of Canada, has been on both sides of the pit. She danced for 15 years with the Royal Ballet of Flanders and other companies, but as a longtime piano student, her interests were split. By the time she retired from dancing in 2018, she’d been studying conducting for a decade.

Ballet, she says, “is such an enormous field to learn, I think many conductors are simply afraid of it. It takes years to understand dancers.”

“You need to hit that high note on the absolute highest moment of their jump, so you need to understand what they’re doing. Then there are five different casts of dancers who perform, and each dancer is different, with a different jump, different musicality, different muscles. Some move faster, some land a jump more quickly.”

Conducting for ballet, Seletskaja adds, is the highest test of technique and control.

“If a male dancer starts his variation or his coda with a huge jump in the air, and that’s where the first note happens, your up beat needs to make sure the orchestra plays exactly at that second — not earlier, not later.”

In other words, autopilot isn’t an option. Throw the risky athleticism of ballet dancers into the mix, and suddenly the conductor is like NASA’s mission control, hawkishly on guard for disaster. A ballerina’s tutu gets stuck on the set, her partner slips on a slick spot, her pointe shoes suddenly go soft and she can’t hold a balance — such facts of ballet life require a conductor to pay attention and improvise, slowing or accelerating to fit the action.

But with so much happening onstage, where is the conductor’s focus?

“Primarily you’re looking from the thighs downward,” says James Tuggle, music director of Stuttgart Ballet, where he has conducted for 23 years. “That’s where they move from. The waist down, or the knees down.”

“Sometimes I’m watching every microsecond,” Tuggle says. Classical works are the trickiest, full of herculean dance passages and jumps, requiring quick variations in tempo, phrasing and dynamics.

“Giselle,” the timeless 1841 ballet (music by Adolphe Adam) about love, betrayal and ghosts rising in the mist, is danced in a simple, open style, with frequent jumps that create a floating effect. Yet this simplicity and buoyancy can be tricky for the conductor.

“It’s like a basketball game,” Tuggle says. “You have some ideas about plays you’re going to make. And then each character jumps differently from another — Giselle, Myrta, Albrecht. You have to watch every second.”

Take the moment in Act 2 when Albrecht, the morally deficient nobleman who’s been bewitched to dance himself to death, begins his coda with a bravura series of entrechat-sixes. These are quick, light jumps in place, with the feet beating together in midair, making Albrecht look like a trapped, winged creature fighting for his life. (Some men prefer a string of brisés, soaring jumps across the stage with a similar fluttery effect.)

The astute conductor employs a little psychology.

“You have to be sure that you keep slightly — very slightly — ahead of him,” Wilkins says. “The worst thing is for the dancer to feel like they have too much time and they have to jump more. It’s very difficult if they feel they have a slow tempo.”

The artistic give-and-take between conductor and dancer comes down to this: making what sounds good and what looks good happen at the same time.

“The music will always sound better if it’s slightly faster,” says ABT principal dancer Herman Cornejo. “And I’m a dancer who likes to move slow. I take my time for the preparation, so my deal in rehearsal is to get a breathing moment before each jump. Not a stop, but a little stretch. Usually it’s a discussion that resolves in us both adjusting a little bit. I mold my body and work on the steps I need to improve so they go with what the conductor is telling me.

“And most of the time,” he adds, “it’s, ‘Move faster.’ ”

“Swan Lake” is rife with trouble spots, particularly in the third act “Black Swan” variations. That’s when the ballerina whips off her 32 fouetté turns — dazzling, but formidable — and a racing pulse from the pit can help her power through.

Prince Siegfried has his own potential quicksand here. At the end of his solo, he whirls into an electrifying series of pirouettes, and the conductor gets ready to rein in the Tchaikovsky for the prince’s spectacular, elegantly controlled finish, and . . .

“ . . . sometimes it doesn’t work out,” says Wilkins, who has seen his share of princes crash to one knee after losing balance, or worse. In any case, the conductor has somehow got to make the music’s ta-dah! fit the dancer’s landing, however unexpectedly it arrives.

“You can usually tell even before they end if it’s going to work or not. Something about the balance of the pirouette,” Wilkins says. “You have to know how to manage those things.”

Out of everyone involved in a live performance, only the conductor can extend a hand, so to speak, to help the dancers get out of trouble.

“It’s an instinctive reaction,” Tuggle says. “You’re coming to the end of a solo and you see they’re behind, so you slow it down. You try to get the music under their feet.

“Or if I feel they can dance a little faster but maybe don’t want to, I might push them. If they’re dragging, I give them some adrenaline. And then I watch carefully to make sure they can keep up. The pacing of a performance is crucial,” he says. “Maybe the audience is dead and you’ve got to wake them up. So I push the dancers.”

Ballet conductors are a hybrid: a dance fan grafted onto an elite music professional. Wilkins started out in his native Australia as a rehearsal pianist for the Australian Ballet. Years of watching dancers prepare their roles were a boon when he moved into conducting, and he never lost his fascination with rehearsals. To this day, if ABT is short a rehearsal pianist, he’ll pop in.

Tuggle volunteered to conduct ballets when he was working with an opera company in Berlin. He never looked back.

“I’m a total believer in the art form,” he says. “I think classical dance is the art form out there, more so than opera. It’s made by people who are in touch with today. Their art is of the time. And the combination of music and dance is extremely powerful.”

Much as they love the art, conductors’ lore is full of picky primas who blame them for every misstep. (“How do you want the music tonight?” one conductor was known to joke about a famous Russian ballerina. “Too fast or too slow?”) The smart conductor doesn’t name names.

The smart dancer picks her battles wisely, if at all.

“I might be one of the only dancers in all of ABT who doesn’t make any big requests,” says Brandt, the ABT soloist. “I think the conductors appreciate me for that reason. . . . If they’re not appreciating your tone, you never know what they may pull on you on performance day!”

She laughs. “I’m not saying they’d ever do anything, though.”

Brandt made her debut as Giselle at the Kennedy Center in February. She’d rehearsed for months, with Wilkins watching since, out of ABT’s three conductors, he was the one scheduled to conduct for her. She’d made one polite suggestion, she says, concerning her hops on pointe across the stage in Act 1.

“It looks more exciting if Giselle does them faster,” Brandt says. “So I gently said, ‘Hey, Ormsby, what about maybe making this part faster, is that okay with you? If you feel like it, maybe we can try it that way one time.’ ”

Then Brandt was thrown onstage a few days earlier than planned, replacing an injured Misty Copeland and dancing with a different partner, Cornejo, after just one rehearsal together.

But as luck had it, Wilkins was in the pit that night.

“It was so much fun,” Brandt says, “and very spontaneous.”

At the curtain call, when she brought Wilkins onstage from the wings to take a bow, as ballerinas do, she gushed to him under the applause: “Thanks so much, Ormsby!” And she led him downstage to bask in the acclaim.

And the spotlight.