DUBAI, United Arab Emirates — Defending champion Stan Wawrinka was upset by Damir Dzumhur 7-6 (4), 6-3 in the first round of the Dubai Tennis Championships on Tuesday.

This was No. 3-ranked Wawrinka's first match since his Australian Open semifinal loss to Swiss countryman Roger Federer. He left Melbourne with a right knee injury and began regular practices only a week ago. Wawrinka said his knee was fine, but suggested he needed more matches to get up to speed.

"In practice, (I) start to be OK the last few days, but today I was missing a little bit of something," he said. "He started also to play a bit better, to put a little bit more first serves in, to put a little bit more pressure on."

Wawrinka raced to a 4-1 lead.

"Three games in, like, six, seven minutes, he was playing outstanding there," Dzumhur said. "I couldn't even touch the ball."

But that was also the point when Wawrinka slowed down and showed signs of becoming tentative, and allowed the Bosnian into the match. In the tiebreaker, Dzumhur went 5-2 up, which was more than enough to secure the first set.

"I was hoping that he's gonna go down with his level of game, and that's what happened," Dzumhur said. "I started to fight, to grind."

Dzumhur bolted to 5-1 in the second set, but became nervous when serving for the match. In the 10-point seventh game, Dzumhur served three double faults, and lost the third break point he faced.

He kept his composure when serving for the match two games later, setting up match point with a forehand cross-court volley, and watched Wawrinka sail a forehand long.