In the fourth game of the third set, Maria Sharapova was pulling Caroline Wozniacki from one side of the court to the other, stretching her forehand, stretching her backhand and stretching her endurance. Wozniacki got to every ball, made every return. She was doing everything the U.S. Open crowd has come to expect of her.
Her final return was a short ball that Sharapova dumped into the net, breaking her serve. And from there, Wozniacki closed out the set and the match, reaching her first quarterfinal in a Grand Slam since Australia in 2012.
Wozniacki is a marathon woman. This fall she will run in the New York City Marathon, and the extra training she puts in for it no doubt allowed her to keep some wind in her sails Sunday. She won the long rallies against Sharapova, and thus the match, 6-4, 2-6, 6-2.
The standout quality of Wozniacki's game is her ability to retrieve. You have to stifle the urge to shout "Fetch!" as she takes off for a wide ball in one direction, skids to a halt and turns to run down one on the other side before maybe scampering to the net for good measure.
"I think my greatest strength is I can go from defense to offense to defense," Wozniacki said. "I think I have done a good job these past few months, finding that balance."
Said Sharapova, "She made me hit a lot of balls. That's always been her strength. But she did extremely well today. She's a great retriever, especially in these types of conditions. I just felt like I went for a little too much."
It was Wozniacki's side-to-side movement that made Sharapova go for it, trying to shorten points in difficult conditions.
Wozniacki said she feels a little guilty for cutting back on her running during the tournament, but the marathon training translates to her game.
"I run a lot already in my training, so to put those extra miles in, I think it helps my head," said Wozniacki, who will run for a charity -- Team for Kids -- in the marathon. "I think it [helped] a lot. Today was a tough battle out there. I had to change my dress. That rarely happens. It was just soaked. Definitely it was helping, because I felt fresh out there and I felt like I could keep going."
After Wozniacki reached the Open final in 2009, losing to Kim Clijsters, and lost in the semifinals the next two years while ascending to No. 1 in the world, it was easy to assume that she would be a regular in the last eight here. But she didn't get past the third round in 2012 and 2013.
This season has been OK, with one victory on hard court in Istanbul, coincidentally on the same day that her erstwhile fiancé, Rory McIlroy, won the British Open.
This summer the 24-year-old Dane keeps running into Serena Williams, losing to her in the quarters in Montreal and the semis in Cincinnati. They are friends and fashionistas together, and Wozniacki is planning on going to Serena's fashion show during New York Fashion Week after the Open.
But first she would like to run into Serena in the U.S. Open final, maybe. "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."
First she runs into Sara Errani in the quarterfinals, and she will keep running and running and running.