The top-seeded Wozniacki won the way she always does — by chasing down hundreds of balls and forcing the other player into making mistakes.
The 14th-seeded Sharapova, trying to return to the quarterfinals at Flushing Meadows for the first time since winning it all in 2006, fought for longer than any of Wozniacki's opponents to this point. But as the pressure of Wozniacki's consistency built, the hard-hitting Russian went for even more, with limited results.
Sharapova wound up making 36 unforced errors. Wozniacki finished with 10 in what was, by far, her biggest challenge of the tournament thus far.
"I knew it wasn't going to be easy," said Wozniacki, who lost to Kim Clijsters in the final last year. "I got a lot of experience from last year, so it definitely helped me today." Wozniacki improved to 18-1 since Wimbledon and stretched her winning streak to 12 matches. Through her first four US Open matches, she has lost a total of 10 games. Maybe most impressive, though, is this stat: She's made 40 unforced errors, compared to 123 by her opponents.
The Dane, ranked second in the world but seeded first because of Serena Williams' withdrawal, eliminated what is largely considered her toughest opponent remaining on her side of the draw.
Next up, "Woz" plays 45th-ranked Dominika Cubulkova, who defeated No. 11 Svetlana Kuznetsova 7-5, 7-6 (4) earlier Monday. In the other quarterfinal on this side of the draw, No. 31 Kaia Kanepi will play the winner of a late-Monday match between No. 7 Vera Zvonareva and Andrea Petrovic.
Kanepi defeated No. 15 Yanina Wickmayer 0-6, 7-6 (2), 6-1 on Monday.
The Wozniacki-Sharapova match was the best show of three afternoon matches in Arthur Ashe Stadium, where earlier No.
3 Novak Djokovic sucked all the life out of the crowd by routing No. 19-seeded Mardy Fish of the United States 6-3, 6-4, 6-1.
Fish's loss left only one American in the draw, No. 20 Sam Querrey, who plays No. 25 Stanislas Wawrinka on Tuesday.
Djokovic, eyeing his third straight US Open semifinal, will play No. 17 Gael Monfils in the quarters. Earlier, Monfils beat fellow Frenchman Richard Gasquet 6-4, 7-5, 7-5.
Since a five-set scare in the first round, Djokovic hasn't dropped a set. Against Fish, who has played two five-setters in addition to doubles over the first week, the Serb was the better, fresher player.
"I'm playing with a lot of confidence," Djokovic said.
"It's definitely great to raise the level of performance toward the end of the tournament. It's been a great couple years for me in New York. Hopefully, I can go on." With countrymen Andy Roddick and John Isner already gone, Fish was hoping to make Labor Day something memorable for his country — an underdog trying to get some momentum, and the crowd, on his side early, maybe channel his inner Jimmy Connors and turn the stadium into his own, personal cheering section.
That never came close to happening against Djokovic, who dictated most points from the baseline and wound up with 30 winners to 13 for Fish. The occasional shout of "Don't give up, Mardy" echoed from the stands, but mostly, this was a flat afternoon and Fish couldn't do much to perk things up.
Midway through the final set in the windblown stadium, Fish changed tactics and tried coming to the net more often. That didn't go well, either. He went 2-for-6 on serve-and-volley points and won only half the 22 points he played at the net.
"I felt so many times today, like even off my first serves, I was sort of fighting to neutralize the point," Fish said. "I was on my back foot quite a bit, even when I was with the wind."
