Croatian veteran Ivan Ljubicic ousted a weary Novak Djokovic 7-5, 6-3 to reach the quarter-finals of the Indian Wells Masters 1000.
While third-seeded defending champion Rafael Nadal on Wednesday booked his quarter-final berth with a 7-5, 3-6, 6-3 triumph over big-serving American John Isner, Djokovic couldn't keep pace with the blistering serves and clean groundstrokes of Ljubicic, a former world number three now ranked 26th in the world.
Ljubicic said he was delighted to end a five-match skid against Djokovic, calling some of those defeats "brutal".
"I'm really happy to be able to beat him finally," said Ljubicic, whose only prior win against Djokovic was their first meeting in Zagreb in 2006.
His most recent defeats to the Serb had come in the first round of last year's US Open, and in the quarter-finals at Dubai last month.
"I served well. My serve helped me, especially in difficult moments... in the second set I was serving even better than the first," said Ljubicic, who gave himself both of his match points in the final game with two of his 13 aces.
Djokovic saved the first, but on the second Ljubicic came up with another big serve that the Serbian could only sail back across the baseline.
"But also two weeks ago in Dubai I was serving unbelievably," Ljubicic said. "You can't beat Novak only with a serve, but it does help you a lot if you can get a lot of free points off that shot."Djokovic said he knew what to expect.
"I don't think any match we play is different," he said. "It's more or less based on the service and returns. As much as I get in the rallies, I think I have more chances to win the point. It wasn't the case today.
"My execution was very bad and he played well when he needed to and he served well when he needed to," said Djokovic, who won his second straight Dubai Open title in February then won both of his matches to help Serbia beat the United States in the first round of the Davis Cup in Belgrade.
Djokovic has looked far from sharp since arriving in the California desert, having to save three match points to subdue Germany's Philipp Kohlschreiber in the third round.
"This is a tournament where I definitely didn't feel comfortable on the court," said Djokovic, the 2008 champion. "It's just because I had a very tiring couple of weeks coming from Davis Cup, which was emotionally very exhausting for me."
The tournament has now lost its top two men's seeds, after world number one Roger Federer was stunned by Marco Baghdatis in the third round on Tuesday.
That left Nadal as the highest-ranked player to make it into the quarters as he withstood a barrage of 22 aces from the 24-year-old American Isner.
World number four Andy Murray was slated to play later Wednesday, taking on Spain's Nicolas Almagro for a quarter-final place.
Baghdatis tried to avoid the letdown a day after his first career triumph over Federer as he tackled Spain's Tommy Robredo, and sixth-seeded Swede Robin Soderling took on ninth-seeded Jo-Wilfried Tsonga of France.
Meanwhile women's fifth seed Agnieszka Radwanska of Poland booked a semi-final berth with a 6-4, 6-3 victory over fourth-seeded Russian Elena Dementieva.
Radwanska has reached her second semi-final of the season without dropping a set, and denied Dementieva a shot at a third title of 2010 - after triumphs in Sydney and the Paris Indoors.
Radwanska awaits the winner of the night quarter-final between second-seeded Caroline Wozniacki of Denmark and China's Zheng Jie.