Marat Safin suffered a third straight defeat following his return from injury, going out in the first round of the Madrid Masters to Jonas Bjorkman.
The Russian, who has played only twice since April because of wrist injury, began well by taking the first set and going up an early break in the second.
However, he became frustrated by a number of foot faults called against him and Bjorkman levelled the match.
Safin visibly tired in the decider and Bjorkman ran out a 4-6 7-5 6-4 victor.
The former US Open champion made his comeback at the Kremlin Cup in Moscow at the beginning of the month, losing to Wayne Black in the first round.
A loss against Fabrice Santoro in Lyon followed last week.
"I've been out for a long time," said Safin. "It's difficult to come back and start winning matches, you lose everything.
"You lose the movement on the court, the eye, the confidence. When you come back you start to pick up these small things step by step."
On a bad day for Russia, Yevgeny Kafelnikov was another first-round loser, retiring after losing the opening set 6-3 against Sweden's Thomas Enqvist.
"I thought I could play, but unfortunately it's tendinitis," said Kafelnikov. "I've had it since losing in the second round at the Kremlin Cup, about two weeks ago."
Mikhail Youzhny also went down 1-6 6-4 6-4 to Spain's David Ferrer.
Jan-Michael Gambill became the fifth American to reach the second round when he defeated Nicolay Davydenko 6-3 6-3.
He joined Mardy Fish, who saw off Britain's Tim Henman in the first match on centre court.
Vince Spadea and Robby Ginepri registered first-round wins on Monday, while second seed Andy Roddick received a bye.
Roddick, the Champions Race leader who could become world number one this week, will face fellow big-server Max Mirnyi after the Belarussian saw off another American, James Blake, 7-5 6-2.
Former French Open champion Gustavo Kuerten was well below his best against in-form Nicolas Massu in the first of the second raound matches, losing 6-3 7-5 to the Chilean.
In the night matches, Albert Costa gave the home crowd something to cheer with a 6-3 7-6 win over Fernando Gonzalez of Chile.
And talented 22-year-old Feliciano Lopez completed a good evening for Spain with a superb 6-4 3-6 6-3 victory over Mark Philippoussis.
The Australian's defeat has put a dent in his hopes of reaching the season-ending Masters Cup in Houston.
He could have moved into eighth place in the ATP Champions Race this week had he reached the semi-finals.
Instead, Philippoussis will remain almost 40 points behind Argentina's David Nalbandian with just two weeks of the regular season to play and two of the eight places in Houston still up for grabs.