Stuttgart:Qualifier Kateryna Bondarenko upset fifth-seeded Ana Ivanovic 6-2, 1-6, 6-1 to reach the quarterfinals of the Porsche Grand Prix.
Meanwhile top-ranked Justin Henin played her first match since winning the US Open and beat Dinara Safina 6-4, 6-1.
Ivanovic, the runner-up at the French Open and a Wimbledon semifinalist, made too many errors against the hard-hitting Ukrainian, who has never advanced past the quarterfinals of a tournament.
"I am not surprised, I prepared well for this tournament," Bondarenko said.
Asked if this was the biggest win of her career, she said: "Yes, it is."
Henin, who also won the French Open this year, took a month off after the US Open.
"I had a nice long rest and it's a good win for me today. It's good to be back," Henin said.
"The first match is never easy and I've been a bit sick the last few days. This is such a strong tournament I have to be on my best from the beginning."
Henin's next opponent will be Elena Dementieva, who beat eighth-seeded Daniela Hantuchova 6-4, 6-4.
Defending champion Nadia Petrova eased into the quarterfinals with a 6-1, 6-3 victory over another qualifier, Michaella Krajicek.
Another Serb, third-seeded Jelena Jankovic, rallied to beat Shahar Peer 4-6, 6-1, 6-3.
The 19-year-old Ivanovic was coming off her third tournament victory this year in Luxembourg, where she also qualified for next month's season-ending WTA Championships in Madrid.
"I am definitely very disappointed, I came here with high expectations," Ivanovic said. "But she played an amazing match, she didn't do much wrong."
Ivanovic in trouble
Ivanovic was in trouble immediately against the 46th-ranked Bondarenko. Ivanovic dropped her serve in the opening game and she kept struggling with her serve throughout the match.
The Serb pulled even at 2-2, following two straight double-faults by Bondarenko, but she didn't a win another game in the first set.
With Ivanovic missing from both sides of the court, Bondarenko hit a service winner to end the set.
Ivanovic called for her coach during the changeover and came out firing in the second, breaking Bondarenko's serve twice to go up 5-0 before winning the set.
"She played better in the second set, but I was also rushing," said Bondarenko, whose older sister Alona is also on the tour.
Another error by Ivanovic, a netted forehand, usually her most reliable weapon, gave Bondarenko the decisive break and a 5-3 lead in the third. Ivanovic saved two match points in the next game, then sent another forehand long to lose.
"I was nervous in the final game and I decided just to hit the ball in," the 21-year-old Bondarenko said.
Bondarenko advanced to her second quarterfinal of the year and will next play Tatiana Golovin, last year's runner-up.
Ivanovic said she was "emotionally drained" after beating Patty Schnyder 6-0, 6-2 Wednesday.
"I was struggling to find my rhythm from the beginning, I was flat," she said.
Jankovic double-faulted to lose the first set but dominated after that.
She wasted two match points, then gained a third on a netcord. Jankovic hit a few deep shots and forced Peer into a backhand error to end the match.
"She doesn't give you any free points," said Jankovic, who is seeking her fifth title of the year. "You have to fight for every point and it's a good win for me."
In the quarterfinals, Jankovic will play Petrova and Bondarenko goes against Tatiana Golovin. Serena Williams, who advanced Wednesday, meets Svetlana Kuznetsova.