A point away from going down two sets to love, Andy Murray's U.S. Open campaign looked sure to come to a premature end on Wednesday, but by the end of the night, and after the surprise defeat of Roger Federer, the Briton's title hopes had soared.

Murray was down a set and 5-1 in the second against Marin Cilic and the contest looked as good as over. But the Croat tightened, Murray seized the opportunity and the match was transformed, with the Scot careering away to win 3-6, 7-6 (4), 6-2, 6-0.

"He got nervous. That was the main difference," Murray said. "I did start playing better towards the end of the second set. And because I was in it, I started to feel that momentum was with me."

Murray was the first man into the semifinals and he would have fully expected to meet five-time champion Roger Federer, who had made it to the last four at Flushing Meadows for eight straight years.

But the Swiss faltered and was beaten by Tomas Berdych 7-6 (1), 6-4, 3-6, 6-3. The Czech is one of the few men on tour who has Federer's measure, having won four of their past seven matches.

Murray had an inkling that Berdych might beat the Swiss. Peppered with questions about Federer during his news conference, Murray — who was sneaking glimpses of the score of the Federer-Berdych match — reminded everyone to respect the Czech.

He was right, and with no Federer and no Nadal, Murray will rarely get a better opportunity to win that elusive first grand slam title, though defending champion Novak Djokovic remained the favorite.

It was an emotional day at the U.S. Open with 2003 champion Andy Roddick heading into retirement with a 6-7 (1), 7-6 (4), 6-2, 6-4 loss to Juan Martin del Potro.

He choked up during an on-court speech at Arthur Ashe Stadium, telling the crowd, "Oh, wow. For the first time in my career, I'm not sure what to say."

"Since I was a kid, I've been coming to this tournament. I felt lucky just to sit where all of you are sitting today, to watch this game, to see the champions that have come and gone," Roddick told the fans. "I've loved every minute of it."

Del Potro joined the fans in standing to applaud after Wednesday's match. He moved on to a quarterfinal against Djokovic, who advanced when his opponent, No. 18 Stanislas Wawrinka, retired because of illness and fatigue while trailing 6-4, 6-1, 3-1.

Djokovic's Serbian Davis Cup teammate, No. 8 Janko Tipsarevic, finished his rain-interrupted 6-3, 7-6 (5), 6-2 victory over No. 19 Philipp Kohlschreiber of Germany, and meets No. 4 David Ferrer of Spain in the quarterfinals.

Murray trailed 5-1 in the second set before breaking twice to come all the way back.

In the tiebreaker, Cilic had a 4-2 lead and a point on his serve, but Murray ran off five straight points to even the match. With royal in-law Pippa Middleton in the crowd, the third-seeded Brit won the last 11 games to wrap up the victory in 3 hours.

"It wasn't necessarily through my great play in the second set why I got back into it," Murray said."But after that, I was hitting the ball much better, and I felt confident at the end of the match. I was returning well, serving well, and moved better at the end. It was good to finish like that."

Four-time major champion Maria Sharapova won her quarterfinal, coming from behind after a rain delay for the second consecutive match and defeating 2007 Wimbledon runner-up Marion Bartoli 3-6, 6-3, 6-4.

Sharapova was down 4-0 on Tuesday when play was stopped. But she wound up improving to 12-0 in three-set matches this year.

"It's a great statistic. It shows that I enjoy the battle no matter what the score is," Sharapova said. "The third set, it's the last set out there, and there's no reason why you shouldn't put everything out there."

No Sharapova-like or Murray-esque theatrics were required by Serena Williams, who has won three of her 14 Grand Slam titles at the U.S. Open. She hit 12 aces in her latest dominant performance, a 6-1, 6-3 victory over 2008 French Open champion Ana Ivanovic.

Williams' semifinal opponent will be 10th-seeded Sara Errani of Italy, who eliminated her good friend and doubles partner, No. 20 Roberta Vinci, in straight sets.