Serena Williams suffered her first defeat since returning to action as she lost 6-2 6-3 to Vera Zvonareva in the Cincinnati Open semi-finals.
Williams looked short of match fitness against Zvonareva
Williams won her first three matches to reach the last four after a six-month break because of a knee injury.
But she could not cope with Zvonareva as the Russian won the first five games and clinched a topsy-turvy second set.
Zvonareva will face Katarina Srebotnik, who beat top seed Patty Schnyder 4-6 6-3 7-6 (8-6), in Sunday's final.
Williams dropped to 139 in the world rankings in her absence, but made an encouraging return to the circuit.
"I think the results are customary for somebody who makes that many unforced errors," said Williams.
"I think I was just off today, but better now than three weeks from now. Every forehand, I think I was aiming at the ball kids or the umpire instead of the court."