US Open, Flushing Meadows
Dates: 30 August - 12 September Start time: 1600 BST
Coverage: Live text commentary on BBC Sport website and mobiles; updates on BBC Radio 5 live; live on Sky Sports
Wozniacki had lost both her previous matches against Sharapova
Top seed Caroline Wozniacki won an enthralling contest of big-hitting against Maria Sharapova to reach the quarter-finals of the US Open.
Wozniacki, 20, gave her title-winning credentials a major boost with a 6-3 6-4 victory over the 2006 champion.
The Dane found the power that many doubted she possessed to beat Sharapova for the first time.
She will face Dominika Cibulkova in the last eight after the unseeded Slovakian beat Svetlana Kuznetsova 7-5 7-6 (7-4).
Wozniacki's status as top seed had been questioned by some as she has yet to win a Grand Slam or even experience a victory against the leading names of the game such as the Williams sisters, Kim Clijsters, Justine Henin or, until Monday, Sharapova.
But the Dane finally overcame the Russian with a combination of her normal relentless recovery skills at the baseline and, in the latter stages, a more aggressive attitude on the backhand in particular.
"I definitely think I've improved a lot, not only physically, but also I believe in myself more," she said afterwards.
It was very hard for me to play one night the second night match and then in one day to play at 11 o'clock
"I believe I can do it. Also I think I can mix up my game a little bit more than I could last year."
Wozniacki got the better of three breaks on her way to taking the first set while Sharapova struggled desperately on serve, making three successive double faults at one stage, and after a closer start to the second set the Dane made the breakthrough in game seven.
By the closing stages, Sharapova was unable to find the consistency to stay with Wozniacki and a final tally of nine double faults and 36 unforced errors to three and 10 from the top seed told the story.
"Even with those unforced errors, I still had my chances and I was one-for-eight on breakpoints," said the Russian.
"Against someone that's playing really well, playing with a lot of confidence, it's really important to take those chances that you have, the very few that come your way.
"I felt like I played a couple of good points and then made an easy error, hit a return long or miss a first serve, give her many looks at second serve returns."
World number 45 Cibulkova had earlier reached her second Grand Slam quarter-final after beating 2004 champion Kuznetsova, who made 42 unforced errors before losing the second-set tie-break.
"She let me play aggressive and she just let me play my game and I played well today," said Cibulkova.
"I was really pumped for this. I knew I could make it and that I could beat everybody in this tournament. I still feel like that."
Kuznetsova had been 4-2 in front in the first set but Cibulkova displayed impressive resolve to fight back and take the set courtesy of a double fault from the world number 12.
And Cibulkova once again displayed her powers of recovery, turning around a 3-1 deficit to lead 5-3 in the second.
The 21-year-old squandered two match points and saw her serve broken in the ninth game as Kuznetsova took the set to a tie-breaker.
But Cibulkova maintained her composure and was sent into raptures when her opponent thumped a forehand wide at match point.
Kuznetsova, on the other hand, was unhappy with the scheduling, saying: "It was very hard for me to play one night the second night match and then in one day to play at 11 o'clock.
"I just I didn't feel good today. I was very flat. I was just fighting with myself and was not doing all the time the things I was supposed to do."
Kaia Kanepi, the 31st seed from Estonia, defeated last year's surprise semi-finalist Yanina Wickmayer of Belgium 0-6 7-6 (7-2) 6-1 and will next face seventh seed Vera Zvonareva, who thrashed Andrea Petkovic 6-1 6-2 in the night session.