Andy Roddick maintained his unbeaten start to the season with a battling four sets victory over Spaniard Feliciano Lopez.
Roddick went into the game on the back of seven straight wins in 2010, including his title success in Brisbane.
However, he was made to fight all the way by Lopez before finally coming out on top 6-7 (4-7) 6-4 6-4 7-6 (7-3) in three-and-a-half hours.
"I feel fine," Roddick said. "I had a longer match today and I'm relieved to get through to the next round."
Roddick has never lost to Lopez in five previous meetings, but the Spaniard possibly missed his best chance to record a win at the Rod Laver Arena.
Crucial
Despite winning the first set on the tie-break, Lopez was guilty of committing 60 unforced errors.
And Roddick, who by comparison committed 21 unforced errors, was able to work his way back into the match - gaining crucial breaks in the fifth game of the second set and the ninth game of the third.
The American, a four-time semi-finalist in Melbourne, will now face 11th seed Fernando Gonzalez after the Chilean came through a five-set epic.
Gonzalez was given a fright by unseeded Kazak Evgeny Korolev before he came storming back to reach the fourth round with a 6-7 (5-7) 6-3 1-6 6-3 6-4 victory.
