Stan Wawrinka blamed a lack of match fitness for his sub-par performance on Tuesday as the defending champion at the Dubai Tennis Championships exited a 7-6 (7-4), 6-3 first-round victim of Bosnian Damir Dzumhur.
The Swiss second seed was playing for the first time since the Australian Open a month ago, when he lost in the semi-finals to Roger Federer.
Since then, he has been dealing with a right knee problem, with the Dubai date creeping up just a bit to quickly for his return.
"I'm quite unhappy to lose in the first round. It's tough, because I played well last year here. I was happy to be back on the ATP Tour after a month," the three-time grand slam winner said.
"I was excited and I wanted to do better this week. But the result is not there, but I think in general it's positive for my tennis."
Wawrinka added: "I started well, but it was tough because I was missing a little bit something. In practice it was starting to be OK the last few days, but today I was missing something."
The Swiss raced off to reach 4-1 in what was looking like a runaway win, but suddenly found himself bogged down as his 77th-ranked opponent seized an opening and ended up taking the first set into a winning tie-breaker.
In the second, Wawrinka's level sunk further, with the Swiss going down a pair of breaks, 1-5.
He got one back in a futile late rally before losing on a first match point after just over an hour.
Dzumhur confessed that he may have been lucky on the day: "I knew that it was not too much about my game. It's about his day. If he's going to play like that (4-1 lead), he's gonna win, I cannot do anything.
"But I was hoping that he's gonna go down with his level and that's what happened. I started to fight, to grind, and I found some way to play, to stay in the game. Playing longer points was giving me more chances.
"This is a big win for me, coming on hard court against a player who likes this surface who won the tournament last year."
Wawrinka said he will decide with his team when to head to Indian Wells for the Masters which begins late next week in California.
Russian Evgeny Donskoy moved into a second-round match with Roger Federer through a defeat of Mikhail Youzhny 6-4, 6-4 while Spain's Fernando Verdasco beat Andreas Seppi 6-2, 7-5.
