ROME — Serena Williams was upset by Patty Schnyder 6-3, 2-6, 7-6 (5) Friday in the quarterfinals of the Italian Open, marking only her third loss this season.
Williams began the year by winning the Australian Open for her first Grand Slam title in two years.
"I just didn't make the shots I was supposed to make," Williams said. "I probably made 50 unforced errors, which is pretty good to get to 7-6 in the third."
The 14th-seeded Schnyder, who was runner-up at this French Open warmup two years ago, also beat Williams in their only previous match on clay. Williams won the other six meetings.
Williams said she does not plan to play again before Roland Garros, which begins May 27.
"I think the best thing for me now is practice," said Williams, whose record fell to 18-3.
Last month, Williams retired from a match in Charleston, S.C., with a groin muscle problem and pulled out of a Fed Cup match with inflammation in her right knee.
"I'm getting there," Williams said of her fitness. "Actually, not winning today is going to work well for me. I'm going to get even more fit."
In the semifinals, Schnyder will face third-seeded Jelena Jankovic, who routed Elena Dementieva 6-2, 6-1.
Williams struggled with her consistency in the first set, missing a series of backhands and committing costly double faults. Schnyder, a left-hander with a crafty all-court game, simply kept the ball in play until the American missed.
Schnyder took a 2-0 lead in the second set before Williams reeled off six straight games to force a third set.
Williams saved a break point in the first game of the third set and two more at 2-2 in the third — the first with a drop-shot winner and the second by stepping into the court to angle a backhand winner.
In the tiebreaker, Schnyder took a 5-2 lead but Williams tied it at 5-5. Williams missed a forehand into the net on the next point and Schnyder hit an approach-shot winner on her first match point.
Both players were bothered at times by the wind, which occasionally whipped up the red clay.
"It was strange conditions. It was really windy. It was a different court than yesterday," said Williams, who beat 11th-seeded Shahar Peer in straight sets on Thursday.
Earlier, Jankovic's powerful groundstrokes proved too much for 10th-seeded Dementieva. Jankovic broke to take a 4-2 lead in the first set and was in control the rest of the way.
"I was feeling my rhythm and I started controlling the points and being very aggressive," Jankovic said.
Jankovic already won a title on clay last month in Charleston, S.C.
"I'm learning how to slide and starting to feel comfortable on clay," said Jankovic, who learned to play on hard courts.
Later, second-seeded Dinara Safina met fellow Russian Svetlana Kuznetsova and No. 9 Daniela Hantuchova faced Anabel Medina Garrigues.