Sluggish Roger Federer relieved to be still in title hunt after second-set lapse

Roger Federer moved into the Australian Open quarter-finals but delivered a performance which again offered hope to his title rivals.

The Swiss beat Tommy Robredo and, while it was always a match he was going to win, the way his concentration disappeared in the second set displayed an element of vulnerability and raised more questions as to whether the world No?2 can defend his title.

He eventually prevailed 6-3 4-6 6-3 6-2 but admitted yesterday's game and the five-set thriller he survived against Gilles Simon last Wednesday had contributed to a "tough" opening week.

"I'm satisfied I'm still in the tournament," he said. "It's been a tough first week with a bit of heat the last couple of matches I played in. I am pretty happy with how I'm hitting the ball. I had a tricky draw and that's why I'm happy I was able to beat all those guys."

Federer accepts it is going to get tougher from here on in, however, and pointed out there were players other than top seed Rafael Nadal who would threaten. "I think Andy (Murray) and Novak (Djokovic) are playing extremely well, and that's why I'm not really looking very far ahead here.

"Robin (Soderling) is playing well; Stan (Wawrinka) same thing, while (Tomas) Berdych hasn't dropped a whole lot of sets or games."

Federer will meet countryman Wawrinka next after he crushed Andy Roddick 6-3 6-4 6-4 with a wonderful display. Roddick has enough trouble dealing with Federer but even Switzerland's second best tennis player proved beyond him. The 19th seed produced a stunning performance of which 16-times grand slam champion Federer will be wary.

Roddick could make no impression and was out-aced 24-9 as Wawrinka ensured a first grand slam quarter-final between two Swiss men since the sport turned professional.

"I'm playing my best tennis," Wawrinka said after extending his winning streak to eight matches.

The contest ended after two hours and 22 minutes when Roddick sliced a weary backhand into the net before gathering his kit and heading off to book a flight home.

"I'm glad I finished healthy," Roddick, who spent much of last year battling injury and illness, said. "First tournament I've done that for a long time. But, you know, there's certainly some work to be done."

Third-seed Djokovic advanced with a hugely impressive win against Nicolas Almagro.The Serbian, the champion here in 2008, withstood everything the big-hitting Spaniard could throw at him before sprinting through the third set to complete a 6-3 6-4 6-0 victory.

Djokovic has flown under the radar so far in Melbourne with all the focus falling on Nadal and Federer and, although his displays in the previous rounds would not have unduly worried the big two, the third seed found his range yesterday."I had a tough opponent, a big hitter, and I could test a couple things in my game: my patience and aggression," he said.

Djokovic will meet Berdych in the quarters after the sixth seed beat Spain's Fernando Verdasco with surprising ease 6-4 6-2 6-3.

The 2010 Wimbledon finalist committed just eight unforced errors in the contest.