Former champion Svetlana Kuznetsova was stunned by Serbian 19th seed Jelena Jankovic 6-7, 6-3, 6-2 in the fourth round of the U.S. Open on Monday.
The 21-year-old Jankovic will face Russian Elena Dementieva in the quarter-finals.
Sixth seed Kuznetsova, the 2004 Open champion, had 46 unforced errors and 41 winners in the two-hour, 19-minute match on the Grandstand.
Jankovic, ranked 20th in the world, blasted 37 winners but had only 24 unforced errors in her first meeting with Kuznetsova.
Fourth seed Dementieva booked a spot in the quarter-finals by defeating France's Aravane Rezai 7-5, 6-4.
Rezai hung in against Dementieva but was ultimately done in by committing 35 unforced errors during the 79-minute match.
Joining Dementieva and Jankovic in the quarter-finals was second seed Justine Henin-Hardenne, who hammered out a warning to her rivals with a crushing 6-1, 6-0 win over Israeli Shahar Peer.
The 2003 champion ripped past 21st seed Peer in just 50 minutes to set up a clash with either seventh seed Patty Schnyder of Switzerland or American Lindsay Davenport, the 1998 champion.
"It was a very good match for me," Henin-Hardenne said.
"I did a lot of serve and volleying today and that helped me to stay aggressive."
Henin-Hardenne had needed three sets to get past Ai Sugiyama of Japan in the previous round but she won 12 of the first 14 points on her way to taking the first set in 23 minutes.
Peer, who was appearing in the fourth round for the first time, had no answer to Henin-Hardenne's power and the Belgian cruised to victory.
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