World No. 1 Roger Federer faced his biggest challenge in the Australian Open this year as the Swiss was forced to the fifth set by Serbia's Janko Tipsarevic on Saturday in the third round.

It took Federer four hours and 27 minutes to finish the marathon with 6-7 (5), 7-6 (1), 5-7, 6-1 and 10-8 win over world No. 49 Tipsarevic, whose best results in the tournament was the second round.

Federer has served strongly with 39 aces but has made 64 unforced errors in the match, compared with 14 and 47 from Tipsarevic.

(Xinhua News Agency January 20, 2008)