The relentless pressure applied by Spanish No.2 seed Rafael Nadal wore down Germany's Philipp Kohlschreiber in a tough four-setter in the Australian Open at Melbourne's Rod Laver Arena in the early hours.

Nadal, whose record suggests he is the greatest threat to Swiss champion Roger Federer sweeping to another grand slam title, won the second round clash 7-5 6-3 4-6 6-2 to stay on track for a possible meeting with the world No.1 in the final.

The match finished at 1.30am (AEDT).

Kohlschreiber, the world No.61, produced tennis which suggested he has the talent to rise above that ranking, trading groundstrokes with the muscular Spaniard on equal terms for what was an enthralling contest for the first three sets.

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