Rafael Nadal endures Australian Open challenge

Defending champion Rafael Nadal endured a nervous night on Rod Laver Arena before eventually fending off the persistent challenge of Philipp Kohlschreiber in four sets at the Australian Open today.

The Spanish second seed was below his best against the 27th-ranked German whose heavy hitting, especially off the backhand side, caused Nadal problems all night.

In the end Nadal simply took his opportunities better to win 6-4 6-2 2-6 7-5 in three hours and 39 minutes, but admitted afterwards he was disappointed with his display.

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

"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."

The left-hander will play big-serving Croatian Ivo Karlovic in the next round after he defeated countryman and 24th seed Ivan Ljubicic 6-3 3-6 6-3 7-6 (7/9).

Reigning US Open champion Juan Martin del Potro was also forced to battle as he edged past unseeded German Florian Mayer 6-3 0-6 6-4 7-5 as the temperature in Melbourne peaked at 32 degrees Celsius.

The Argentinian had needed five sets to overcome veteran American James Blake in the previous round and, after being stunned by Mayer in the second set, had to rally from 4-2 in the fourth to avoid going the distance again.

"Today, especially in the second set, I felt very confused with my game," Del Potro admitted.

"After that I improved a little bit but by the end I finished the match playing very good points."

Del Potro will face a seed for the first time in the fourth round where Marin Cilic awaits after he recovered from losing the first set to 19th seed Stanislas Wawrinka and win 4-6 6-4 6-3 6-3.

Fifth seed Andy Murray continued his march through the early rounds with a trouble-free 7-5 6-1 6-4 win over 64th-ranked Florent Serra.

Murray is yet to meet a player inside the top 50 and has coasted through the opening week.

"I'm happy to have won in three sets in all of the matches," he said,

"I'm happy to save as much energy as possible. Today was hot so it was nice to get off the court quickly."

Big-serving American John Isner upset 12th seed Gael Monfils 6-1 4-6 7-6 (7/4) 7-6 (7/5) and he will play Murray in the fourth round.

Isner joined countryman Andy Roddick in the last 16 after the former world number one came from a set down to edge a closely-fought match with Spain's Feliciano Lopez 6-7 (7/4) 6-4 6-4 7-6 (7/3).

Roddick's next match is against 11th seed Fernando Gonzalez, the 2007 runner-up, who needed five sets to beat Kazakhstan's Evgeny Korolev 6-7 (7/5) 6-3 1-6 6-3 6-4 in a match that lasted three hours and 42 minutes.