Although never a real scare, the threat from the Australian 18-year-old during a 6-2, 7-5, 6-3 win was such that the Spanish world number one admitted he will have to improve, especially with his main rivals in ominous form.
Andy Murray and Robin Soderling, potential semifinal opponets for Nadal, galloped into the second week. Murray, runner-up to Roger Federer last year, dismantled Spain's Guillermo Garcia-Lopez 6-1, 6-1, 6-2 while Soderling trounced Czech qualifier Jan Hernych 6-3, 6-1, 6-4.
Tomic's expected defeat ended home hopes in the singles after fifth seed Samantha Stosur was beaten by Czech Petra Kvitova 7-6, 6-3 -- a defeat she was at a loss to explain.
Nadal, bidding to become only the third player to hold all the majors at once, was forced out of his comfort zone by Tomic. Playing with the freedom of a man with nothing to lose and roared on by a partisan crowd, the 199th-ranked teenager rattled the Spaniard at the start of the second set, firing rasping forehand winners about the court to take a 4-0 lead.
The scowl on Nadal's face deepened as he mixed up his game to regain the lost ground, darting to the net more frequently and peeling sweat-drenched off his torso at the changeovers.
While Tomic was an extremely long-shot for the men's title, his compatriot Stosur was considered a genuine contender to end Australia's 33-year wait for a singles champion here. The fifth seed was unable to meet the weight of expectation that had helped draw 77,121 people to Melbourne Park, however, and crumpled under the pressure after leading the first set tiebreaker 5-3.
Stosur picked Kim Clijsters to win the title and the three-times US Open champion continued to glide through the women's draw, beating French birthday girl Alize Cornet 7-6, 6-3.
Women's second seed Vera Zvonareva reached the fourth round with a 6-3, 7-6 win over Lucie Safarova, keeping her on track for a maiden grand slam title.
Murray and Soderling are both yet to drop a set as they raced towards a quarterfinal showdown. "It was good," fifth seed Murray said after an 82-minute breeze. "Served well. Hit the ball clean from the back. That was it."
Soderling, looking every bit the top-four player he has become, said a Nadal-Federer final was by no means a formality. Murray faces Juergen Melzer next after the Austrian went through against former runner-up Marcos Baghdatis who retired with a finger injury in the fourth set.
Two men's seeds toppled early. Tenth-ranked Mikhail Youzhny crashed out 6-4, 7-5, 4-6, 6-4 to Canadian qualifier Milos Raonic and 2008 runner-up Jo-Wilfried Tsonga lost 3-6, 6-3, 3-6, 6-1, 6-1 to Ukraine's Alexandr Dolgopolov. Cilic, a semifinalist last year, set up his date with Nadal by beating American John Isner 4-6, 6-2, 6-7, 7-6, 9-7.
The Croatian sealed victory after four hours and 33 minutes -- some seven hours short of Isner's record match against Nicolas Mahut last year at Wimbledon -- and the players embraced at the net.
