Camila Giorgi sprang an upset to defeat four-time champion Caroline Wozniacki 6-4, 6-2 on Wednesday and reach the quarter-finals of the WTA Connecticut Open, a final warm-up for the US Open.
The Italian saw off the former world number one in 78 minutes to book a last-eight date with Spain's Garbine Muguruza, who eliminated Chinese qualifier Peng Shuai 6-2, 3-6, 6-3 in another second-round match.
The unseeded Giorgi also ousted Wozniacki in last year's US Open, but lost their only other meeting this year at Eastbourne.
Wozniacki, whose best Grand Slam showing was a 2009 US Open runner-up effort, won the title at New Haven from 2008 to 2011, but saw her record at the Yale University event dip to 24-3.
The 24-year-old Dane's only prior losses since Wimbledon came in three-set battles with world number one Serena Williams in Montreal and Cincinnati.
"I knew I was going to get limited break chances and when I did get them, I didn't convert," Wozniacki said. "I knew I had to be aggressive out there and try to push her back, but I didn't manage to do that. She played well and I didn't."
The defeat does allow Wozniacki a few extra days to prepare for the year's final Grand Slam, which starts on Monday.
"I would have loved to have been here longer, but it wasn't to be this year," Wozniacki said. "Now I just need to take the positives out of it. I get a few extra days to rest up and practice for the US Open."
Wimbledon finalist Eugenie Bouchard also failed to make it to the quarter-finals.
Australian veteran Samantha Stosur briskly ousted the third-seeded Canadian 6-2, 6-2.
Stosur next faces Belgian Kirsten Flipkens, who beat Germany's Andrea Petkovic 4-6, 7-6 (7/4), 7-6 (8/6).
Thursday's other two quarter-finals were already set. Slovakian Magdalena Rybarikova, who ousted top-seeded Simona Halep, will take on American Alison Riske, and second-seeded Wimbledon champion Petra Kvitova will face fellow Czech Barbora Zahlavova Strycova.