NEW YORK (AP) -- Caroline Wozniacki trusts her stamina so much that she plans to return to New York in two months to run a marathon.
Maria Sharapova, usually the one wearing down opponents in the third set, sure couldn't keep up on a steamy Sunday at the U.S. Open. Wozniacki won 6-4, 2-6, 6-2 in 2 hours, 37 minutes to get back to her first Grand Slam quarterfinal in more than two years - and get back in the headlines for reasons other than her personal life.
"The season for me has been a little bit up and down," she said in quite an understatement, "and it's so nice to kind of start feeling like I'm playing the way I want to."
Because of the heat, the players received a 10-minute break before the final set; Sharapova returned to the court late, arguing with the chair umpire after receiving a time violation warning. Perhaps sensing that she was fresher than the five-time major champion, Wozniacki later complained that Sharapova was dawdling between points.
Her tardiness seemed to swing the Arthur Ashe Stadium crowd's support squarely in Wozniacki's favor. When the 10th-seeded Dane broke Sharapova at love to go up 3-1 in the final set, she got a standing ovation from the fans and waved her arms to egg them on. Sharapova had appeared to hit a winner three times on that game's final point only for Wozniacki to somehow chase down the ball. Finally, Sharapova put a volley into the net.
Wozniacki mixed in just enough aggression with her signature defense to keep the pressure on Sharapova in the final set.
"She's very good at getting a lot of balls back and making you hit another one," Sharapova said. "In the end, I went for a little too much."
She insisted the conditions didn't bother her. Sharapova had been 17-6 in three-set matches this year, including her come-from-behind second-round victory here.
The fifth-seeded Sharapova's loss leaves No. 1 Serena Williams as the only woman remaining of the top six. Ninth-seeded Jelena Jankovic was also upset, losing 7-6 (6), 6-3 to 17-year-old Swiss Belinda Bencic.
With mentor Martina Hingis cheering from the stands, Bencic became the youngest U.S. Open quarterfinalist since Hingis herself in 1997.
After a sloppy first set, Sharapova was painting the lines in the second. Wozniacki seemed to spend most of it watching in dismay as one of Sharapova's 22 winners whizzed by.
Wozniacki said she told herself before the third set to go for her shots.
"If I'm going to lose," she recalled thinking, "at least I'm going to do it with dignity."
She closed out the match by breaking Sharapova's serve again with a backhand winner. About a half-hour later, thunderstorms halted play with second-seeded Roger Federer down a break in the first set to Marcel Granollers.
Federer acknowledged the two-hour delay helped him regroup. While Granollers won the first set, Federer dominated the rest of the way, winning 4-6, 6-1, 6-1, 6-1.
Unlike the women's draw, the men's side didn't lose a top-10 player until Sunday, when fourth-seeded David Ferrer was upset by Gilles Simon in the third round 6-3, 3-6, 6-1, 6-3. Sixth-seeded Tomas Berdych and No. 7 Grigor Dimitrov also advanced.
Dominic Thiem, 20, made his first Grand Slam round of 16 with a straight-set win over 19th-seeded Feliciano Lopez. Another first was achieved in the women's draw by Peng Shuai, who had never been to a major quarterfinal before beating 14th-seeded Lucie Safarova 6-3, 6-4.
Wozniacki will next face 13th-seeded Sara Errani, who ended the run of qualifier Mirjana Lucic-Baroni with a three-set victory.
As a 19-year-old, Wozniacki made the 2009 U.S. Open final, losing to Kim Clijsters, and reached No. 1 in the world the next year. But she hadn't been back to a Grand Slam quarterfinal since the 2012 Australian Open.
In the meantime, she was best known for getting engaged to star golfer Rory McIlroy - then getting dumped in late May after wedding invitations had gone out.
Wozniacki lost in the first round at the French Open soon thereafter and was upset in the fourth round at Wimbledon. She had been playing much better since, though, winning her first title in nine months at Istanbul then dropping a pair of three-set matches to Williams.
Wozniacki also announced a month ago that she planned to run the New York City Marathon on Nov. 2 for charity, somehow squeezing in training during a busy fall season. Seems to be working out well mentally and physically on the tennis court.
"Kind of clears my head," she said of the extra running. "I feel more free when I go on court."
Wozniacki plans to stick around New York after the U.S. Open to attend Fashion Week - including her pal Williams' show - and get in some running in Central Park. The marathon prep has gone on hiatus the last few days, though.
As Wozniacki deadpanned, "I have a pretty big tournament here that I kind of want to try and win."
Roger Federer advances in 4 sets at U.S. Open
NEW YORK (AP) -- Roger Federer regrouped after a fortuitously timed rain delay to move on at the U.S. Open in four sets.
The second-seeded Federer was a game from losing the first set to Marcel Granollers in the third round Sunday when play was stopped because of lightning.
After they returned to the court two hours later, Granollers won the set, but Federer dominated the rest of the way in a 4-6, 6-1, 6-1, 6-1 victory.
Drenched with sweat on a humid night, Federer acknowledged afterward that the break helped him. He started serving better in the final three sets.
"He was doing a lot of things really well," Federer said later. "It was just, for me, going to be one of those things to like weather the storm and see if he could maintain that level of play or not and if I could lift my game up and see how that matched up. I think overall it worked out great at the end."
The 42nd-ranked Granollers was looking to make the fourth round at the U.S. Open for the second straight year.
Federer next faces 17th-seeded Roberto Bautista Agut of Spain, who beat Adrian Mannarino 7-5, 6-2, 6-3. The 17-time Grand Slam champion has dropped one set through three matches.
"I feel very explosive, quick," Federer said.