Updated

By Ian Ransom

MELBOURNE (Reuters) - World number three Novak Djokovic and U.S. Open champion Juan Martin del Potro kicked off their Australian Open preparations with easy first-round wins at the Kooyong Classic in Melbourne Wednesday.

Del Potro cruised to a 6-3 6-3 victory over Croatian Ivan Ljubicic, before Serbian Djokovic made light work of experienced German Tommy Haas 6-2 6-3 at the eight-man invitational event.

Despite blustery conditions at the Kooyong Lawn Tennis Club, Del Potro was in fine touch for his first hit-out of the season, although he may hope for tougher encounters this week after Ljubicic repeatedly gifted him key points with unforced errors.

"The weather conditions were tough, a lot of wind," Del Potro told reporters. "I returned very good, I served very good so that's important for this kind of match, this kind of surface. It's a good victory in the beginning of the season, of course."

After breaking the 24th-ranked Croatian in the opening game, Del Potro cracked two forehand winners to set up two set points at 5-3, and was duly handed the set when his opponent double-faulted.

Ljubicic raised his game after conceding an early break in the second, but fluffed a chance to break back later and eventually succumbed after saving three match points.

"It wasn't all that bad actually. Probably the most disappointing thing is that I didn't feel bad at all and I still lost 6-3 6-3," he said.

LESS THAN AN HOUR

The 2008 Australian Open champion and top seed Djokovic needed less than an hour to defeat 18th-ranked Haas, racing to a one-set lead after breaking the German early and then carrying the momentum into the second.

The 22-year-old Serbian, who eschewed season-starting tournaments in the Middle East, appeared in top fitness after coming off high-intensity training camps in the Italian Alps and the Middle East.

"I feel much better, feel fresh ... I just need a couple of matches under my belt before I go to Melbourne Park," he said.

Djokovic may face more of a work-out in the semi-final against Spanish world number nine Fernando Verdasco, who defeated Chilean Fernando Gonzalez 7-5 6-1 in an occasionally farcical match later Wednesday.

Verdasco, who made his presence felt in the very first game by cannoning a first serve into his opponent's crotch, was taken to 5-5 before the Chilean appeared to self-destruct, conceding the first break and set in a hail of unforced errors.

Jo-Wilfried Tsonga will take on Del Potro in the other semi-final after dismantling Robin Soderling 7-6 6-1.

British world number five Andy Murray, craving a last hit-out before his bid for a maiden grand slam at Melbourne Park next week, will play 25th-ranked American Sam Querrey in an exhibition match Thursday.

(Editing by Patrick Johnston)