Monaco:Roger Federer lost to Olympic gold-medal doubles partner Stanislas Wawrinka 6-4, 7-5 on Thursday in the third round of the Monte Carlo Masters.
Federer looked sloppy throughout the match and faced 14 break points.
Wawrinka set up his first match point with a deep shot into the corner that the second-seeded Federer failed to return, and he clinched victory with a backhand pass down the line.
The 13th-seeded Wawrinka, who plays alongside Federer on Switzerland's Davis Cup team, will next meet qualifier Andreas Beck of Germany in the quarterfinals.
Federer looked shaky from the start, having to save a break point in his opening service game, before Wawrinka got the decisive break in the seventh game. Federer then sent an easy forehand into the net to give Wawrinka the first set.
The two players traded breaks to open the second set and Federer, who accepted a wild card to play in the tournament after originally planning to skip the clay-court event, had to save two more break points at 15-40 in the seventh game as Wawrinka pressured his unusually weak forehand.
Wawrinka then needed another four chances before breaking Federer again in the 11th game to serve for the match at 6-5. Although Wawrinka wobbled, Federer missed two break points and failed to force a tiebreaker.
Federer was playing in his first tournament since getting married to longtime girlfriend Mirka Vavrinec on Saturday.
In other matches, the seventh-seeded Fernando Verdasco beat No. 10 David Ferrer 6-2, 6-1 in an all-Spanish match, and Beck rallied to beat Juan Monaco, Argentina, 3-6, 6-2, 7-5.