By Ian Ransom

MELBOURNE (Reuters) - An unenthused Rafael Nadal played down his form at the Australian Open and said he would need more time to regain his confidence after digging himself out of a hole against Philipp Kohlschreiber.

Defending champion Nadal, who has not missed the last 16 of a grand slam since the 2005 U.S. Open, has set himself modest goals at Melbourne Park and was not feeling more bullish about his prospects after being stretched to a 6-4 6-2 2-6 7-5 win over the German in the third round.

"Well, it wasn't bad," Nadal told reporters after the three and a half hour match.

The Spaniard had not dropped a set in his first two matches at Melbourne Park and appeared set to do the same against 27th seed Kohlschreiber, but the German threw caution to the wind at two sets down to scramble back to force a fourth.

The tactic came undone at 5-5 in the last, however, an unforced error giving Nadal the break and allowing the Spaniard to coolly serve out and seal the match with a sweetly-struck winner.

Nadal, who defeated Roger Federer in a classic five-set final last year, has struggled to reach his fist-pumping best since being struck down by knee tendonitis after the French Open last year.

He has not won a tournament since April and was bundled out of the ATP Tour Finals in London after losing three straight matches there.

"If I lose here next round, I am gonna have chances to play well during all the season," said Nadal.

"So the Australian Open is a very important tournament, but it is not the end of the world. You have a lot of time to get your full confidence, to play well."

"Always a really difficult opponent, no, because the match is decided in a few points.

"So the thing is to concentrate hard on my serve all the time and try to convert the small opportunities that I can have on the return. That's it."

(Editing by Alison Wildey)