Defending Australian Open champion Rafael Nadal endured a nervy night on Rod Laver Arena before eventually fending off the persistent challenge of Philipp Kohlschreiber in four sets.
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.
The left-hander will play big-serving Ivo Karlovic in the next round after the Croatian defeated countryman and 24th seed Ivan Ljubicic.
Kohlschreiber defeated two left-handers, Horacio Zeballos and Wayne Odesnik, en route to the third round and while he lost the opening two sets against Nadal he fully tested his more-fancied opponent.
Nadal grabbed an early break of serve in the opening set which proved decisive, although he had to fend off seven break points to stay ahead and clinch it in an hour and three minutes.
Nadal broke immediately in the second set, coming back from 40-love down, to get his nose in front.
The set followed a similar pattern to the first with Kohlschreiber probing away at the Nadal serve but proving unable to convert his break-point opportunities.
The German's doggedness was finally rewarded in the third set.
Nadal struggled with his first serve and Kohlschreiber pounced with some impressive winners as the defending champion grew increasingly tetchy.
The seven-time grand slam winner was twice broken and continually looked to his courtside entourage for inspiration as he lost the set.
Kohlschreiber sensed an upset was possible and matched Nadal from the baseline as the match developed into a dogfight.
Nadal looked like he had taken the edge with a couple of wonderful forehand passing shots to break, which finally brought him to life with a double fist-pump celebration.
But again Kohlschreiber battled back to immediately break back and square the set at 4-4.
An untimely poor service game at 5-5 cost Kohlschreiber as he three times sent wild forehands wide and was again broken.
Nadal did not squander the chance this time as he served out the match, with a cross-court winner sealing his passage to the last 16.