NEW YORK -- With the New York City Marathon just nine weeks away, Caroline Wozniacki got a head start on Sunday. She met Maria Sharapova's corner-to-corner barrage with a combination of relentlessness and nerve, chasing down balls with a speed that could get her considered for a start with the elite women come November.
After three sets, the 10th-seeded Wozniacki ousted fifth-seeded Sharapova 6-4, 2-6, 6-2, advancing to face 13th-seeded Sara Errani in the quarterfinals. On the court, she asked fans to get behind her marathon charity, Team For Kids.
Understandably, though, she's put her training on hold this week.
"I have to say that I feel really guilty because the last few days I have told myself I better just cut down on my running," Wozniacki said. "I have a pretty big tournament here that I kind of want to try and win."
This was Wozniacki at her best. Her father and coach, Piotr Wozniacki, said it's because she is back to practicing like she did when she last reached the quarterfinals here in 2011.
Why hadn't she been doing that the past few years?
"The situation with Rory," said Piotr, referring to her former boyfriend and professional golfer Rory McIlroy, who called off their engagement in May. "So you understand this is not easy. First time, very hard for Caroline's heart."
Here, the father and native Polish speaker paused to clear his throat.
"Caroline now looking for tennis," he continued. "Practice very good, Caroline playing more aggressive."
After winning the PGA Championship earlier in this month, McIlroy said breaking up with Wozniacki helped his golf game. And it looks like Wozniacki is getting the same competitive bump. They even both won tournaments on the same day last month, when McIlroy won the British Open and Wozniacki won the Istanbul Cup.
Is it now Wozniacki's turn to win a major?
With the way she's playing, it's sure possible. Wozniacki beat Sharapova -- a champion here in 2006 who was playing well in New York -- for just the third time in eight meetings.
Wozniacki looked resurgent, aggressive and accurate in a way she hasn't recently in New York. She reached the final here in 2009 and then two semifinals, but never won the US Open or any other major.
The match started in humid heat on Arthur Ashe Stadium, but after Sharapova took the second set, clouds rolled in and the air began to cool. With rain on its way, the wind gusts made serving the ball tricky.
"Today was a tough battle out there," Wozniacki said. "It was humid. It was hot. I had to change my dress. That rarely happens. It was just soaked."
Sharapova took a break between the second and third sets, and was assessed for a time violation upon her return. She appeared to argue the decision before returning to the baseline to receive serve.
Serving down 2-1, Sharapova faced a triple-break point. Controlling the point from the start, Sharapova sent Wozniacki side to side, but Wozniacki got everything back and eventually forced a Sharapova unforced error at the net. The crowd gave a pumped-up Wozniacki a standing ovation.
"She's a great retriever, especially in these types of conditions," Sharapova said. "I just felt like I maybe went for a little too much."
Wozniacki is on the opposite side of the draw from both of those players.
"I told Serena I'm pretty tired of her," Wozniacki said. "Twice she beat me in three sets. I said, 'Can you just get out of my way?' We just laugh about it."
Wozniacki will stay in New York after the US Open to run in Central Park and attend Serena Williams' show at Fashion Week. Both have helped her game. Williams was a fierce and visible ally in the weeks after Wozniacki's engagement ended, and the running is having an obvious impact on her game.
"It's hard work, you know," Wozniacki said. "I run a lot already in my training, so to put those extra miles in, I think it helps my head. Kind of clears my head. I feel more free when I go on court."
And it shows.