Roger Federer has claimed that losing the second-set tie-break was crucial following his shock defeat to Andreas Seppi in the third round of the Australian Open.

A 6-4 7-6 4-6 7-6 victory for Seppi condemned Federer to his earliest exit from the tournament for 14 years, and the second seed was left in no doubt what the turning point was against the Italian.

"I knew how important that second-set tie-breaker was, so clearly that hurt," Federer, who had won all of the 10 previous meetings with Seppi, told members of the media.

"I just somehow couldn't play my best tennis today and that was also due to Andreas playing great tennis. I just had an overall feeling that I couldn't get the game going.

"I was playing well in practice, I played well in Brisbane, I'd like to say I peaked too early. It just broke me to lose that second set."

Federer had reached nine successive semi-finals at the Australian Open before this year.