Roger Federer said it was a "special moment" to return to the big stage as he passed a first-round test at the Australian Open on Monday.

The 17-time Grand Slam champion, back in action after a six-month injury layoff, downed his one-time junior rival Jurgen Melzer of Austria 7-5, 3-6, 6-2, 6-2 in just over two hours at Rod Laver Arena.

The Swiss 17th seed will now play American qualifier Noah Rubin in the second round.

"It was a special moment walking out on the court. A special moment when you get to match point and when you win it," Federer said of his comeback.

"I think those three components make it special when you're coming back. It's already great to just be here, trying to play with the guys. I'm happy with the more relaxed attitude and also the success came easier."

Federer, 35, is bidding to become the second oldest man in the Open era to win a Grand Slam title, after Australian Ken Rosewall.

Asked about the constant debate about his eventual retirement, Federer said: "It doesn't surprise me because I've been talking about retirement for seven years.

"Naturally that's the perfect opening for people to ask that question yet again, think to themselves, 'Why more?' I get it. It's fine. I'll keep answering it."

Federer, playing in his 69th major, has dropped to 17th in the world rankings after a knee injury restricted him to just seven Tour events last year.

He dropped out of the world's top 10 for the first time in 734 weeks in November and his ranking is at its lowest since May 2001.

Federer fell behind to an early break against Melzer in the opening set but once he gained his playing rhythm he broke back and then again in the 11th game.

Melzer, who grew up in the juniors with Federer, evened the match by taking the second set, but the Swiss legend whipped through the third in 28 minutes with the Australian crowd cheering his every winning point.

Federer finished off in style with two breaks of serve to run a convincing winner.

Stan says he's sorry

Meanwhile, Stan Wawrinka apologized for slamming a ball at Martin Klizan after he survived a tense five-setter to reach the Australian Open second round.

Wawrinka, a three-time Grand Slam champion, fought back from a break down in the final set to overhaul the 35th-ranked Slovak 4-6, 6-4, 7-5, 4-6, 6-4 in a match that lasted three and a half hours.

There was a dramatic moment in the final set when Wawrinka fired a volley at a defenseless Klizan, who had conceded the point after a rally and was standing at the net.

The Swiss fourth seed quickly jumped over the net to offer his apologies as Klizan sunk to his knees in pain.

"That was, for sure, a tough shot for him. The thing is there are some players they fake you, and you stop playing and then they just put up the racket," Wawrinka said.

"I had already missed some easy ones. For me the most important thing was to run straight over to him. I just wanted to make sure he was OK."

Klizan preferred not to pass judgement on Wawrinka but said the Swiss could have hit his volley anywhere on the court.

"I stopped playing. He could play anywhere, the whole court," the Slovak said. "He could play anywhere on the court, but he hit me."