(CNN) -- Argentina's Juan Martin Del Potro made a disappointing comeback from injury at the Thailand Open in Bangkok on Tuesday, where he was defeated 7-6 6-4 by Olivier Rochus of Belgium in the opening round.
The 22-year-old has not played on the ATP Tour since losing in the fourth round of the Australian Open in January, after sustaining a wrist injury which has seen the former world number four slip to 36 in the world rankings.
But despite serving 16 aces during the match, the 2009 U.S. Open champion's return to the game was cut short by world number 78 Rochus in just under two hours.
A foot shorter than his two-meter, Rochus came through a close first set and a break down in the second to book his place in the second round of south-east Asian tournament where he will play Kazakhstani Mikhail Kukushkin.
After the match fifth seed Del Potro was full of praise for his victor and said he was just happy to be playing again despite the loss.
"I played a good match," Del Potro told the official ATP website. "I had my chances in the first-set tie-break and he played some great points. He served very good, which was important on this kind of surface. He played very well today.
"I'm just happy to be back on the circuit and I hope I get better and better."
The result opens up the draw for world number one Rafael Nadal, who would have faced Del Potro in the quarterfinal.
The Spaniard will be playing in the tournament for the first time, after arriving in the Thai capital on Tuesday.
The newly crowned U.S. Open champion will face Belgian qualifier Ruben Bemelmans in a second round match on Wednesday.
Meanwhile in Tuesday's other first round matches, Germany's Rainer Schuttler defeated Brazil's Ricardo Mello, Guillermo Garcia-Lopez of Spain beat German Michael Berrer, and world number 13 Jarkko Nieminen saw off home favorite Danai Udomchoke.