Rafael Nadal and Roger Federer eased into the Australian Open's second round on Monday as local teenager Bernard Tomic stole the show with an epic five-set upset of Fernando Verdasco.

Tomic, his country's top-ranked men's player at 38, dug deep as he came from two sets down to oust the experienced Spanish 22nd seed in a four hours-plus thriller on a sweltering Rod Laver Arena.

The 19-year-old produced the finest performance of his fledgling professional career to reel in Verdasco in only his third five-setter.

While Tomic was showcasing the future, the game's giants Nadal and Federer, with 26 grand slams between them, cruised through in straight-sets victories.

Nadal brushed aside America's Alex Kuznetsov 6-4, 6-1, 6-1, despite revealing later that he feared his bid for another Australian title was over before it started after suffering searing knee pain ahead of his first match.

The Spanish world number two was only able to take to the court for his early evening match after intensive treatment including physiotherapy and anti-inflammatory drugs.

Federer spent just 1hr 38min on Rod Laver Arena in administering a 7-5, 6-2, 6-2 win over the 172-ranked Alexander Kudryavtsev.

While Federer played in the evening, Tomic and Verdasco slugged out their dramatic match in 34 Celsius (93 Fahrenheit) temperatures.

Tomic again showcased his enormous potential after he became the youngest man in 25 years to reach the quarter-finals of last year's Wimbledon.

"Anything's possible if you keep trying," Tomic said. "Same thing happened at Wimbledon when I was in the second round. I was losing two sets to love down and made the quarters.

"Anything is possible. Can't always give up. You can learn about yourself, and, yeah, how in the future you can play."

Verdasco looked on course to wipe Tomic in straight sets, powering through the opening two sets before the Australian broke the Spaniard in the ninth game of the third set to sight a glimmer of hope.

And Tomic grew stronger in the heat, while Verdasco showed more signs of weariness and he took the match into a fifth set.

"Had I not done that fitness (training) the last two, three months, there's no way mentally you can be out there in that heat and turn around in a match like that and win," Tomic said.

"I think it was all fitness, the way I've been preparing the last few months. It's all paid off."

In a gripping final set Verdasco needed his big serving to fight off Tomic before he was broken in the 11th game, allowing the teenager to serve out for a courageous win.

In the second round Tomic will play American Sam Querrey, who beat French wild card Kenny de Schepper in straight sets.

Former US Open champion Juan Martin Del Potro needed four sets and three hours to reach the second round in overcoming French world number 91 Adrian Mannarino 2-6, 6-1, 7-5, 6-4 on Hisense Arena.

The Argentine giant will now face Slovenia's Blaz Kavcic in the second round after Kavcic's straight-sets win over Britain's James Ward.

Elsewhere, Czech seventh seed Tomas Berdych accounted for Spaniard Albert Ramos in four sets, Swiss Stanislas Wawrinka eased past Frenchman Benoit Paire in straight sets and American eighth seed Mardy Fish downed Luxembourg's Gilles Muller for the loss of 10 games.

Spanish 10th seed Nicolas Almagro knocked out Poland's Lukasz Kubot, 1-6, 7-5, 6-3, 7-5 and Germany's Tommy Haas ousted American qualifier Denis Kudla in four sets.

David Nalbandian went through when Finland's Jarkko Nieminen, who won last week's Sydney International after coming through qualifying, retired in the second set with strained stomach muscles.