Melbourne: World number one Rafael Nadal and last year's finalist Andy Murray eased into the Australian Open second round on the back of injury retirements on Tuesday.

Nadal advanced after Marcos Daniel retired during the second set with a knee injury, while Murray got through when Karol Beck succumbed to shoulder trouble while trailing in the third set.

Former US Open champion Juan Martin del Potro also made a winning return to Grand Slam tennis after missing nearly all of last season with a wrist injury.

Spanish top seed Nadal, bidding for his fourth straight major title to complete a non-calendar year Grand Slam, was leading 6-0, 5-0 when Brazil's Daniel retired with a painful left knee.

Nadal was only on court for 47 minutes and the nine-time Grand Slam champion sought more work on his service after the injury-shortened match.

"I practised for half-an-hour after the match. Hopefully my serve is going to be fine," he said.

Nadal was sympathetic with Daniel's plight after he was forced out with a knee injury in his quarter-final against Murray at last year's Australian Open.

"He's a really nice guy and I'm really sorry for him," he said of the 93rd-ranked Daniel. "I wish him all the best for the recovery. Hopefully it is nothing really important."

Nadal, who extended his Grand Slam winning streak to 22, said he was not concerned about missing an opportunity for match practice.

"Save energy or not, I think the way that the match ended doesn't make a big difference to me," he said.

Daniel took a medical timeout after losing the opening set in 19 minutes and looked a dejected figure as he hobbled around centre court unable to chase down Nadal's volleys.

After his sixth service break, Daniel walked to the net and conceded defeat to Nadal.

"I was practising two days ago and I made a bad movement, I felt a very strong pain," Daniel said. "I was feeling really bad. Today I knew it was going to be really tough."

Nadal, who is recovering from an illness which struck him during the Qatar Open, said it was difficult to assess his form after the abbreviated match.

"It's difficult to say if I played really well or played bad," he said.

"I think I played all right. I played some good shots, some long shots. The serve can be a little bit better.

"I have to improve more (on serve) if I want to play well here. So that's it. For the rest, forehand and backhand, I felt okay."

Nadal is chasing his second Australian title and his 10th Grand Slam trophy in Melbourne.

Murray, who lost to Roger Federer in last year's Australian final, was leading 6-3, 6-1, 4-2 when Beck conceded defeat after an earlier medical timeout to treat his inflamed serving shoulder.

There was also joy for 2009 US Open winner del Potro, who won his first Grand Slam match since suffering the wrist injury at last year's Australian Open.

Argentine del Potro, who has an injury-protected ranking to make the main draw of the season-opening major, downed Israel's Dudi Sela, 7-6 (15/13) 6-4, 6-4.

It was plain sailing for most of the other leading men's seeds on Tuesday with Spain's David Ferrer (7), Russia's Mikhail Youzhny (10), Austrian Jurgen Melzer (11) and Croatia's Marin Cilic (15) all advancing to the next round.