DUBAI - Novak Djokovic returned to his quest for titles after one of the biggest disappointments of his career with a hard-hitting, straight sets success before a packed stadium at the Dubai Open. The 6-3, 6-3 victory over Denis Istomen, a talented world number 53 from Uzbekistan, was ideal competitive rehabilitation for the seven-time former Grand Slam winner after the loss of his Australian Open title to Stanislas Wawrinka in the semi-finals at Melbourne.The ambience was lively enough to summon adrenaline, the opposition capable enough to create good rallies, and the outcome encouraging enough for Djokovic to feel he can win his fifth title here. If he does, he will equal the record of Roger Federer, whom he should meet in Friday's semi-finals. But, even more important for Djokovic is to feel that the "food for the soul" he says he took from childhood haunts during a five-week break is now feeding his self-belief.He projected more than 20 unforced errors, but often served well, too, despite missing some chances to finish rallies, and yet he always won the points and games that really mattered in a colourfully patchwork performance. "My game isn't where I want it to be," Djokovic admitted. "But I am still happy with this start. It's just the match situation - it's quite different from the practice court. You have thousands of people watching you and it can be mentally tough. And not having competed for so long, it takes a toll. My body feels it a little bit. But I will get back to work. It's work and I love it at the same time." Djokovic next plays Roberto Bautista Agut, the world number 51 from Spain, while Federer will take on Radek Stepanek, the former top ten player from the Czech republic who has won deciding matches in Davis Cup finals twice. The tournament's second seed however did not survive. Juan Martin Del Potro, the former US Open champion who became the ATP Tour's comeback player of the year after recovering from a career-threatening wrist injury, was struck down by a similar ailment.The courageous and usually hard-hitting Argentine lasted little more than an hour and only one set in the Dubai Open, before requiring lengthy treatment on his left wrist after which he called it quits against Somdev Devvarman, a wild card entry from India. "My wrist is hurting a lot and, you know, everybody knows what's happened to me four years ago with my other wrist."It's hurting all the time, sometimes less and sometimes a little more. But it's hurting, and I have been in contact with my doctor all the time. He's trying to keep me motivated to keep playing, but I know what is my limit playing on court. Today was enough. I cannot say that (it will be surgery) yet - but I'm feeling similar pains to the other hand and what I felt four years ago. It's not really positive for my future."Tomas Berdych, the third-seeded Czech who reached the final last year, may be one of those who benefits from Del Potro's misfortune as they were seeded to meet in Friday's semi-finals. Berdych scored his 13th win in 14 matches, a 6-3, 6-4 success against Marius Copil, a Romanian qualifier. "Always you can make from basically any kind of situation that you can put pressure on yourself, but that's probably not the best idea to do," said Berdych, when asked how much he focused on maintaining the streak. "So I'm just trying to profit from that, trying to build up on the form, try to bring the confidence as far as I can, and really just go one by one. That's not really counting the matches."