— Two sets in arrears to Roger Federer and hurtling rapidly toward a 14th consecutive loss to the Swiss master, Mikhail Youzhny turned to Wimbledon’s Royal Box on Wednesday and asked Andre Agassi for advice.

Agassi erupted in laughter. The Duke and Duchess of Cambridge, better known as William and Kate, shared a giggle. And even Youzhny had to smile, knowing that on this day not even sage words from a tennis legend could derail Federer’s bid to reach Wimbledon’s semifinals.

Centre Court, after all, is where the 30-year-old Federer has done his most artful work, winning six of his record 16 major titles on its lawn with seemingly effortless grace.

His time there Wednesday was brief. Federer needed just 92 minutes to dismiss the earnest but outclassed Russian, 6-1, 6-2, 6-2.

Moments later on Court 1, Novak Djokovic, the tournament’s defending champion, advanced almost as easily, defeating Florian Mayer, 6-4, 6-1, 6-4, to complete the semifinal pairing that tennis fans have longed to see since the draw was unveiled, one that pits Wimbledon’s six-time champion against its current title-holder.

Federer and Djokovic have met 26 times in their careers but never on grass. Federer holds a 14-12 edge, but the 25-year-old Djokovic has won the last three encounters.

“Roger has been at the top of the men’s game for so long,” Djokovic said of Federer, who was the world’s top-ranked player for 285 weeks. “This is where he won six titles. He definitely wants to prove to himself, and to everybody else, that he can win it once again.”

If Federer and Djokovic staged displays of grass court superiority in their respective matches Wednesday, Scotland’s Andy Murray staged one of fortitude against David Ferrer of Spain.

Theirs was a physically exhausting, mentally grueling match that included three tiebreaks and a rain delay. After the two traded blows for 3 hours 52 minutes, Murray prevailed, 6-7, (7-5), 7-6 (8-6), 6-4, 7-6 (7-4), to reach his fourth consecutive Wimbledon semifinal.

Instead of two-time champion Rafael Nadal, who has halted the Scot’s charge the last two years, Murray’s semifinal opponent will be Jo-Wilfried Tsonga of France. An exuberant and powerful player, Tsonga leapt in the air and pumped a triumphant fist upon clinching his 7-6 (7-5), 4-6, 7-6 (7-3), 6-2 victory over Philipp Kohlschreiber.

The semifinals are Friday, and will mark Tsonga’s second consecutive trip to Wimbledon’s final four. He advanced at Federer’s expense last year, clawing back from a two-set deficit.

Wednesday against Youzhny, Federer looked every bit in his prime, showing no trace of the back ailment that flared up earlier in the week.

He breezed to victory with near pinpoint stroke precision, winning the point 88 percent of the time that he landed his first serve and committing just 13 unforced errors.

“I’ve been playing well for many months,” said Federer, who boasts a 109-16 record on grass. “I’m happy that going into the semis I’m not tired, I’m not injured — I’m not anything. I’m fresh and ready to go.”

While the lopsided affair didn’t qualify as riveting entertainment, Federer was rewarded with a prolonged ovation from the Royal Box, which was studded with past champions such as Rod Laver, Billie Jean King, Steffi Graf and Agassi—unabashed admirers, all.

If Wimbledon’s Royal Box holds elites, the grassy mound outside Centre Court, known as Henman Hill, is home to Wimbledon’s groundlings. There wasn’t an unoccupied patch on it for Murray’s match, with thousands arrayed on blankets to cheer on the Scot via a giant TV screen.

Neither Murray, who has yet to tap his full potential, nor the 30-year-old Ferrer, who has more than maximized his, has won a major.

Murray’s pursuit looked doomed late in the second set. He had lost the opening set in a tiebreak, and Ferrer was poised to take a two-sets-to-none lead, serving at 5-4. But Murray broke back. With Ferrer suddenly playing conservatively, Murray attacked, blasting two huge serves to win the set in a tiebreak.

A relentlessly hard worker, Ferrer fought back in the fourth set. The score was knotted at five games each when rain halted the proceedings.

Centre Court has a retractable roof, but tournament officials are reluctant to deploy it. London’s rain has a way of moving on, and the high-tech roof doesn’t close on a dime; it takes nearly 40 minutes. So the court was covered with a tarp, and the showers stopped soon thereafter.

The score deadlocked at six games each; another tiebreak ensued. Murray crushed a forehand winner to reach set point before blasting his 18th ace to seal the victory.

After raising a clenched fist to the crowd, Murray sank in his courtside seat and flung his head back, not hiding his exhaustion and relief.