On Labor Day, Rafael Nadal had to play four sets to get rid of Sam Querrey, then Tuesday brought another labor day (that wasn't planned on the US holiday calendar) as Roger Federer and Novak Djokovic had to play five sets to get through to their quarter-finals.

In the case of Djokovic, the net was simply there to hold him up, otherwise he was sure he would have keeled over while trying to complete a television interview following his exhausting 4-6 6-2 6-3 5-7 6-3, three hour 44 minute fourth-round victory over Tommy Robredo of Spain.

Third-seeded Djokovic had entered the match still tired and sore from a three-hour third-rounder against Marin Cilic that ended well after midnight Monday. A quite afternoon at the US Open suddenly turned frenetic as matches on both the Arthur Ashe and Louis Armstrong courts extended beyond their expected time allotments.

Thousands of fans awaited the start of the evening matches between second-seeded Jelena Jankovic and Sybille Bammer and eighth-seeded Andy Roddick and No.11 Fernando Gonzalez. They gathered around the giant fountains just inside the USTA Billie Jean King National Tennis Center and watched the latter stages of Roger Federer's five-set duel with Igor Andreev on a giant overhead screen - Flushing Meadows' version of Wimbledon's Henman Hill.

Meanwhile, fifth-seeded Nikolay Davydenko was across the grounds suffering through a demoralising loss to 130th-ranked Gilles Muller of France. At one point, Davydenko and Muller and Federer and Andreev were locked in simultaneous tie-breakers, Federer for the second set and Davydenko for the fourth.

With Andreev serving at 5-6 seeking a two-set lead, after already saving two set points, Federer hit a high forehand volley that sat up long enough for Andreev to get a piece of it. But the forehand pass the Russian had in mind clipped the top of the net and sailed wide, levelling the match at a set apiece.

Over on Armstrong, Davydenko - who had not dropped a set in his first three matches - was down two sets to one to Muller, a qualifier who had won three matches just to get into the main draw and then back-to-back five-setters to reach the fourth round. Davydenko squandered four set points in the 10th game of the fourth set but then held serve to force the tie-breaker.

After blowing another three set points that would have taken the match into a fifth, Davydenko double-faulted to give Muller his third match point, which he won when the Russian smacked a forehand that hit the top of the net, bounced up, and dropped back on his side to give Muller a 6-4 4-6 6-3 7-6 victory.

"I think it was the most exciting tie-breaker I've ever played in my whole life," said Muller, who became the first quarter-finalist from Luxembourg at any major in the Open era and the lowest-ranked quarter-finalist here since 136th-ranked Nicolas Escude of France in 1999. "I have nothing to lose but, on the other hand, I have a lot to win. It's easier to deal with the pressure to win something than to lose something.''

As Muller and Davydenko were heading toward the locker room, all eyes shifted back to Ashe, where Federer suddenly looked in control, taking the third set with ease. But once again the net intervened, this time in Andreev's favor, as the Russian hit a backhand slice that ticked the tape and fell over for a winner, giving him a crucial break for 3-1 in the fourth. It was a lead he would hold to force a fifth set.

With the crowd inside the stadium roaring - and the fans outside now sprinting back over to Armstrong, where Jankovic was cruising past Bammer 6-1 6-4 in a quarter-final that was moved to make room for Roddick and Gonzalez on Ashe - Federer broke serve in the second game of the deciding set.

As the clock ticked toward the three-hour mark, Federer broke on his third attempt when he chased down a tricky drop shot off Andreev's racket and turned it into a delicate lob winner. But even when the four-time Open champion went 3-0 up he never seemed in complete control.

With 60 unforced errors, many of them off the forehand, Federer lacked the impenetrable confidence that has defined him here. Serving at 4-2 in the fifth, the Swiss second seed faced four more break points in an 18-point game that he finally won with a backhand down-the-line pass off yet another Andreev drop shot. He then hit a service winner to go 5-2 in front.

When he closed out the three hour 32 minute 6-7 7-6 6-3 3-6 6-3 win two games later, Federer unleashed a giant roar then tossed a toothy grin toward his friends' box while the public address system blared "Still The One" by Orleans.

"Down a set and in a tie-breaker for the second, there's danger written all over that situation," said Federer. "But it's not really that much time to waste, you know, thinking about that kind of stuff. You just hope that it's going to turn your way. It did, so I'm happy. I think it was really entertaining for the fans. Being part of those dogfights is fun."

Federer now meets Muller for a spot in the semi-finals while Djokovic will take on Roddick, who needed just one hour 27 minutes to demolish Gonzalez 6-2 6-4 6-1.