Wimbledon champion Petra Kvitova was ousted by 145th-ranked qualifier Aleksandra Krunic of Serbia 6-4, 6-4 in the third round of the US Open, joining a long list of women's upset victims.
The 21-year-old Krunic, who aims to graduate from university in Serbia this year with a degree in economics, registered the shock result when the error-prone Czech whipped a cross court forehand just wide of the line.
Kvitova, who made 34 unforced errors in the 98-minute match against the quick-moving Serb, became the fifth seed from the top eight to be dismissed joining Simona Halep (2), Agnieszka Radwanska (4), Angelique Kerber (6) and Ana Ivanovic (8).
Lucic-Baroni ousted second-seed Halep, Italy's Sara Errani posted her first career win over Venus Williams and Swiss teen Belinda Bencic ousted sixth-seeded German Kerber.
Croatian Lucic-Baroni, a 32-year-old qualifier ranked 121st in the world, dismissed Romania's Halep 7-6, 6-2 to reach the fourth round for her best grand slam result since a 1999 run to the Wimbledon semi-finals.
Bencic, 17, last year's French Open and Wimbledon junior champion, defeated Kerber 6-1, 7-5 to reach the round of 16 in her US Open debut.
The Swiss, who made it to the third round at Wimbledon, vowed not to be satisfied with her Flushing Meadows success.
Errani, loser of all three previous singles matches against Williams in straight sets, outdueled the seven-times grand slam winner in a thrilling third-set tiebreaker to win their roller-coaster clash 6-0, 0-6, 7-6.
Ninth-seeded Jelena Jankovic of Serbia, 29, crushed Sweden's Johanna Larsson 6-1 6-0, and 28-year-old Peng Shuai of China registered another upset when she eliminated 28th-seed Roberta Vinci of Italy 6-4, 6-3.
Also advancing was 10th seed Caroline Wozniacki of Denmark, a 6-3, 6-2 winner against 18th seed Andrea Petkovic of Germany.