LOS ANGELES — At the climactic final moment of the 89th Academy Awards, when Faye Dunaway read the name of the film printed on the card in front of her — “La La Land!” — there were two people, standing on either side of the stage, who knew immediately that a different film, “Moonlight,” was the actual winner of the Oscar for best picture.

But no one else knew, not until the ceremony was interrupted nearly two full minutes later, after multiple “La La” creators had already given acceptance speeches. It was an agonizing unspooling of awkwardness that a Pricewaterhouse Coopers executive described to reporters Monday as “a human error.”

As Tim Ryan, chairman and senior partner of the accounting firm that has long been the keeper of the Oscar envelopes, described the scenario, one of the so-called Oscar “ballot leaders” simply handed co-presenter Warren Beatty the wrong envelope — with a spare copy of the card awarding Emma Stone the best actress prize for her role in “La La Land.”

The resulting confusion drew the spotlight away from the winners, and to an arcane set of protocols that have been rehearsed over more than eight decades. When disaster struck, from a viewer’s perspective, it appeared that the players froze.

“One or the other of those accountants could have been at the mic in 30 seconds,” said Paul Sheehan, executive editor of the Hollywood awards site Gold Derby. “I think if we were in shock, so were they — but they had one job, and they didn’t do it.”

The Oscars are the granddaddy of awards ceremonies, decades older than the Grammy Awards, Emmys, Tonys, or Golden Globes. They have cultivated, over the years, a carefully constructed pageantry and ritual: the presenters, the build-up, the suspense. The envelope, please.

The ritual has defined modern awards culture: there should be shock, but not horror; tears, but not sad ones — and a sense that the grandest cinematic prize cannot be tampered with or fouled up.

Until Sunday, that is, when Dunaway declared the wrong best picture for the first time in the ceremony’s 89-year history. The PwC accountants, Martha Ruiz and Brian Cullinan, walked on stage to confer with “La La Land” producer Jordan Horowitz, who eventually grabbed the microphone: “I’m sorry, no, there’s been a mistake. ”

This was not a joke, he quickly emphasized. But for the two people who hold the paramount responsibility of guarding and distributing the envelopes, it was something of a nightmare — precisely the sort of screw-up that Ruiz and Cullinan had worked scrupulously to avoid.

The ballot leaders oversee the vote-tallying process, identify the winners for each category, select the cards for the winners and seal them into their respective envelopes — but not before they memorize each winner in each category.

“Ideally, we like to have everything completed several days before the show. That last day is when Brian and I will start memorizing the winners of each category and start quizzing each other,” Ruiz said in a recent interview published by the academy’s public relations arm. “It’s that extra measure to make sure it really is only to our memory at that point, to make sure that everything’s accurate.”

On the day of the ceremony, Ruiz and Cullinan carry matching briefcases, each filled with a full set of 24 top-secret winners envelopes. The accountants travel to the theater separately, escorted by police, to ensure that at least one set of envelopes arrives on time.

During the ceremony, Ruiz and Cullinan stand on opposite sides of the stage. Because award presenters might enter from either side of the stage, there are two copies of each envelope — one set stationed at each possible entrance. Ruiz and Cullinan hand the envelopes to the presenters.

“It doesn’t sound very complicated,” Cullinan said, “but you have to make sure you’re giving the presenter the right envelope.”

Which, of course, did not happen Sunday night, when Cullinan handed Beatty the wrong envelope.

By the time the situation was sorted out, the “La La Land” team had suffered the embarrassment of delivering speeches for a prize they didn’t win, and the stunned cast and crew of “Moonlight” was left with little opportunity to respond to their rightful victory.

“The moment they heard Faye Dunaway say ‘La La Land,’ the two [accountants] should have been sprinting to the middle of that stage, and saying ‘I’m very sorry Mr. Beatty and Ms. Dunaway, you were given the wrong envelope,’” Sheehan said.

He said he was shocked as he watched the sequence unfold. It seemed clear that Beatty, who opened the envelope, was confused by the card inside; Dunaway seemed to think Beatty was stalling purely to build suspense.

“Our expectations of them are unfair,” he said. “They’re older, it’s live television. Dunaway isn’t wearing glasses — she sees the words ‘La La Land,’ maybe she doesn’t see ‘Emma Stone.’ I don’t fault them. To me, the entire responsibility lies at the feet of those two accountants, who let the whole thing play out far too long.”

Sunday’s gaffe likely has other organizations checking and rechecking their procedures. A spokesman for the Television Academy, which presents the Emmy Awards, said only that it works with Ernst & Young “to oversee this part of the process, and is confident with their safeguards.”

William Ivey Long, the most recent chairman of the American Theater Wing, which created the Tony Awards, was immediately sympathetic to the Oscars plight. “The same thing happened to me,” he said Monday. “The same thing!”

Long was the recipient of a 1982 Tony for his costume-design work on the musical “Nine.” At the time, those awards were revealed at an off-stage ceremony and then reaffirmed on stage. So Long had already been told that he was the winner — but while sitting in his auditorium seat, he heard presenter Hal Linden call out the costume designer for “Dreamgirls.”

“My heart sank and my stomach dropped to the floor,” Long recalled. Then “Nine” star Raul Julia yelled from his seat, “No! It’s William Ivey Long!” It turned out that the presenters’ cue cards contained all of the nominees, in alphabetical order, with the winner underlined. The presenter had merely read the first name and hadn’t read down far enough to see Long’s name marked.

Despite Sunday’s debacle at L.A.’s Dolby Theater, “Moonlight” director Barry Jenkins was magnanimous about the snafu when he met reporters backstage.

“I noticed the commotion that was happening, and I thought something strange had occurred. And then I’m sure everybody saw my face. But I was speechless. . . I’ve watched the Academy Awards, and I’ve never seen that happen before,” he said. “And so it made a very special feeling even more special, but not in the way I expected.”

No one offered a reason for the confusion, he said. But he appreciated the gracious way Beatty tried to reassure him amid the chaos. “He came upstairs and he walked over to me. . . He’s like, ‘No, Barry Jenkins has to see the card. I need him to know.’”

Caitlin Gibson and Monica Hesse reported from Washington.