Defending champion Rafael Nadal reached the fourth round of the Australian Open 2010 on Friday - but was made to work hard for his victory.

The Spaniard was far from his best on Rod Laver Arena as he eventually beat Philipp Kohlschreiber of Germany in four sets.

Nadal struggled with his first serve at times, especially in the third set, and found Kohlschreiber's heavy hitting hard to deal with throughout the match.

Nadal eventually won 6-4 6-2 2-6 7-5 in three hours and 39 minutes to set up a fourth round tie against Ivo Karlovic of Croatia.

"The most important thing is I won, so I am happy for that," said Nadal afterwards.

"I am less happy about my game, what I was practising but everybody has a not very good day.

"I think I played much better in the fourth set than the rest of the sets. The second set a few moments I played well too. The first set and the third, I played bad.

"I need to play a little bit more aggressively for next matches."

Karlovic booked his place in the next round after he defeated Ivan Ljubicic 6-3 3-6 6-3 7-6 (7/9).

Nadal remains second favourite in the Men's singles market at 7/2 behind Roger Federer (5/2), who is in action on Saturday.

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