Andy Roddick, John Isner in quarters

NEW YORK -- At one point, Andy Roddick looked up and saw a fan scaling a chain-link fence behind tiny Court 13, hoping to catch a peek of the 2003 U.S. Open champion's victory Thursday.

At another point, a baby's loud cries provided a distraction at the 584-seat venue.

"At least," Roddick deadpanned later, "there wasn't a baby crying on the fence."

It was that sort of day at this most unusual U.S. Open.

Rain finally gave way to sun in the morning, but chaos still managed to reign. A crack near a baseline in the tournament's second-biggest stadium let water seep through, halting Roddick's already twice-delayed match against David Ferrer until they were moved to a court often used by juniors.

And because of showers earlier this week, the U.S. Tennis Association extended the tournament, delaying the men's final by 24 hours to Monday at 4 p.m. ET. The women's final was shifted from Saturday night to Sunday at 4 p.m.

Amid all of Thursday's goings-on -- which also included complaints about the schedule both before and after it was changed; talk by Roddick and others about forming a union; and treatment by a trainer for both No. 1 Novak Djokovic and his opponent, who eventually quit, then apologized to Djokovic -- at least there was plenty of tennis played, quite a change from Tuesday's total washout and Wednesday's 15 minutes of action.

Roddick, defending champion Rafael Nadal, Andy Murray and John Isner all won to reach the quarterfinals. On the other side of the men's draw, Djokovic and Roger Federer set up a semifinal showdown; it's the fifth consecutive year they'll meet at the U.S. Open and a rematch from this year's French Open, where Federer handed Djokovic one of his two losses in 2011.

Given the delays, the 21st-seeded Roddick was eager to get going against the fifth-seeded Ferrer somewhere -- anywhere, really.

They got in less than 10 minutes Thursday before Roddick pointed out a damp spot in Louis Armstrong Stadium that made it too dangerous to play. He and Ferrer headed back to the locker room while workers spent an hour trying to dry the area. At 12:30 p.m., the players returned with tournament referee Brian Earley to inspect the area.

Roddick pointed out that the spot still was wet and said to Earley, "Can you tell us why you brought us out here? ... How hard is it to not see water? ... What are we doing here?"

As he walked to the sideline, Roddick shook his head and said: "I'm baffled right now. Absolutely baffled." He shoved his racket in his bag and walked off the court, as some fans jeered.

Roddick, Ferrer and Earley then spoke in a hallway of 10,103-seat Armstrong stadium.

"Put us on 13. Thirteen's open. Let's go play. I don't care where we play," Roddick said.

Within minutes, the decision was made to switch courts, sending fans running and pushing their ways over to the metal bleachers at Court 13, and the match eventually resumed a little before 1 p.m.

Not much more than two hours later, Roddick was high-fiving front-row spectators after wrapping up his 6-3, 6-4, 3-6, 6-3 victory.

He hadn't played anywhere at Flushing Meadows other than the main court, Arthur Ashe Stadium, since 2002, a run of 39 consecutive U.S. Open matches there.

On Thursday, he found himself on a court where he last played singles in 1999, losing a first-round junior match.

"I didn't think Court 13 was in my future. ... But extenuating circumstances, I guess," Roddick said.

"I thought the atmosphere was great. People packed in," added Roddick, who will play Nadal next. "I'd rather play a smaller court and have it packed, than playing a bigger court and have it a quarter full."

Elsewhere, No. 2-seeded Nadal beat 68th-ranked Gilles Muller of Luxembourg 7-6 (1), 6-1, 6-2 in Ashe; No. 4 Murray eliminated 84th-ranked Donald Young of the United States 6-2, 6-3, 6-3 in the Grandstand; and No. 28 Isner got past No. 12 Gilles Simon of France 7-6 (2), 3-6, 7-6 (2), 7-6 (4) on Court 17.

Murray plays Isner, who reached the first Grand Slam quarterfinal of his career.

In the night's last match -- which was interrupted by rain for 1½ hours in the first set -- Federer beat No. 11 Jo-Wilfried Tsonga 6-4, 6-3, 6-3 to reach the U.S. Open semifinals for the eighth year in a row. Five of Federer's 16 Grand Slam titles came in New York.

At Wimbledon in late June, Tsonga upset Federer in the quarterfinals after dropping the first two sets. Until that loss, Federer was 178-0 when taking a two-set lead in a Grand Slam match. Federer did not let Tsonga get back into Thursday's rematch, saving a key break point at 2-2 in the third set, then breaking in the next-to-last game when Tsonga double-faulted.

"It's true, the Wimbledon match does come back into your mind, especially when he's got break point in the third. ... But I was able to come out of that one," Federer said.

He is 3-1 against Djokovic at Flushing Meadows. Plus, Federer ended Djokovic's 43-match winning streak by beating him in a thrilling French Open semifinal this year.

Djokovic reached his sixth consecutive major semifinal and improved to 62-2 this season, advancing when his opponent, No. 20 Janko Tipsarevic, stopped playing while trailing 7-6 (2), 6-7 (3), 6-0, 3-0. Tipsarevic had his left hamstring bandaged by a trainer at 5-0 in the third set.

Djokovic needed his own visit from the trainer for treatment on a bloody left big toe after sliding to get to a drop shot in the fourth set's opening game. They're good friends and Davis Cup teammates, and they met for a long hug at the net when Tipsarevic conceded; he said he told Djokovic he was sorry for stopping.

On Roddick's side of the draw, one of the men's finalists faced the prospect of playing four best-of-five-set matches in four days, back-to-back-to-back-to-back, something Nadal called "not fair." Now the men will get Sunday off.

Nadal also raised a bigger concern: Players should have more say about how Grand Slam events are run.

"The problem is we don't have enough power in these kind of tournaments," Nadal said. "That's what have to change very soon."

Others, including Murray and Stosur, echoed that sentiment, saying commercial interests outweigh player interests in tennis, and Roddick weighed in on the idea of forming a union.

"The fact is that the players feel frustrated. The players feel they're not protected enough, I guess," Djokovic said. "So this is maybe a turning point for all of us."

Information from The Associated Press was used in this report.