Novak Djokovic opened the defence of his Dubai Championships title with a straight-sets victory over Denis Istomin, while second-seeded Juan Martin del Potro had to retire from his first-round match.

Top-seeded Djokovic, who is making only his second appearance this year after reaching the quarter-finals of the Australian Open, was a 6-3, 6-3 winner over 54th-ranked Istomin of Uzbekistan.

Del Potro was not so fortunate, being forced to retire against Somdev Devvarman of India after losing the first-set tiebreaker 7-6.

Since winning the Sydney title last month, Del Potro has been struggling with a left wrist injury that has conjured up memories of similar pain he experienced in his right wrist four years ago.

In 2010, the year after he won the US Open, he played only three tournaments before and after surgery on his right wrist.

Del Potro was fighting back tears in Dubai when he came to talk to the media after his retirement.

"I don't feel really well,'' he said. "My wrist is hurting a lot and everybody knows what happened to me four years ago with my other wrist. It was really tough to play today. I tried everything. I cannot be the player I would like to be."

Third-seeded Tomas Berdych extended his winning streak to eight matches with a 6-3, 6-4 win over Romanian qualifier Marius Copil. Fifth-seeded Jo-Wilfried Tsonga of France secured a 6-2, 6-4 win over Victor Hanescu of Romania.

Source: AP