(CNN) -- Caroline Wozniacki underlined her status as women's top seed with a battling straight sets 6-3 6-4 victory over former champion Maria Sharapova in their last 16 clash at the U.S. Open on Monday.
The 20-year-old Dane withstood the customary onslaught from Sharapova to emerge victorious after just under two hours of compelling action on the Arthur Ashe Stadium Court at Flushing Meadows.
Sharapova, desperate for another grand slam title after clawing her way back up the rankings following shoulder surgery, made an impressive start but an astonishing string of double faults in the fourth game saw her fall 3-1 behind.
In customary style she immediately broke back with her best tennis of the match, but then lost her own service again leaving Wozniacki to serve out for the first set.
The second was again a tight and closely fought affair, but in the seventh game Sharapova chose the wrong moment for her ninth double fault and she was behind again.
Wozniacki held to leave Sharapova to serve to stay in the championship and the former world number one was forced to bravely save a match point before closing to 4-5.
But Wozniacki, beaten by Kim Clijsters in last year's final, made no mistake when she served for the match, closing it out with the first of two match points.
It was her first win over former world number one Sharapova.
She will now play Dominika Cibulkova in the quarterfinals after the Slovakian's impressive 7-5 7-6 win over another former champion Svetlana Kuznetsova of Russia.
Ranked 45, Cibulkova is the lowest ranked player remaining in the draw, but performed well above her status to outlast Kuznetsova.
Also through to quarterfinals is Estonia's Kaia Kanepi, who came from a set down to beat Belgium's Yanina Wickmayer 0-6 7-6 6-1 in a thriller on the Louis Armstrong Stadium Court.
Wickmayer, a semifinalist at Flushing Meadows last year, looked to be cruising to victory as she swept the opening set without the loss of a game, but 31st seed Kanepi battled back to level on a tiebreaker and swept through the decider.
Russia's Vera Svonareva was also victorious on day eight, advancing 6-1 6-2 at the expense of Germany's Andrea Petkovic.
It was a comfortable win for the seventh seed, who will now play in her first U.S. Open quarterfinal.