Five-time champion Serena Williams reached her first Grand Slam quarter-final of the year at the US Open on Monday, setting up a clash with Flavia Pennetta in a duel between the two oldest women left in the draw.
World number one Williams, eased past world number 50 Kaia Kanepi, 6-3, 6-3, for a fourth win over the Estonian.
"It's my first quarter-final of the year at the majors -- at last I did it," said the 32-year-old American, who had fallen in the fourth round in Australia, the third round at Wimbledon and suffered a second round French Open exit.
"It was a tough match today. I wanted to stay relaxed and told myself that whatever happens, Serena, you're still in the doubles."
Italian 11th seed Pennetta, also 32, reached her fifth quarter-final in New York with a 7-5, 6-2 victory over Australian 29th seed Casey Dellacqua.
Meanwhile, Maria Sharapova crashed out of the US Open Sunday while 17-year-old Belinda Bencic became the youngest women's quarter-finalist since 1997 giving Switzerland a double boost after Roger Federer had moved into the last-16.
She will next face 13th-seeded Italian Sara Errani who ended the magical run of 32-year-old Croatian qualifier Mirjana Lucic-Baroni 6-3, 2-6, 6-0.
"It means so much to me," said 2009 runner-up Wozniacki, who reached the semi-finals in 2010 and 2011 but hadn't been past the third round at Flushing Meadows the last two years.
"It's been a bit up and down for me this season. To win today against a champion like Maria is an unbelievable feeling."
Sharapova, the 2006 champion, admitted she had been outplayed.
"I thought she played really well. She made me hit a lot of balls. That's always been her strength," said the Russian.
Bencic, 17 and ranked 58th, dismissed former world number one Jelena Jankovic 7-6 (8/6), 6-3 to become the youngest US Open quarter-finalist since Martina Hingis won the title in 1997 at the age of 16.