The Swiss top seed, playing his first tournament since his shock

second-round exit at Wimbledon, dug deep to claim the third set for a 7-6 (7/4), 3-6, 7-5 quarter-final victory.

Mayer, 45th in the world compared to Federer's fifth ranking, fired down six aces, three times more than the Swiss star, but Federer was strong where it counted, saving three of the five break points he faced in the third set.

Federer has a 32-4 event record in Hamburg, where he won the title in 2002, 2004-05 and 2007, then finished runner-up in 2008 to Rafael Nadal.

The Swiss star will now face Argentinian qualifier Federico Delbonis in Saturday's semi-finals.

German second-seed Tommy Haas made a quarter-final exit when he lost in straight sets, 6-2, 6-4, to Italian 12th-seed Fabio Fognini, who claimed his first ATP tournament win at Stuttgart last week.

Fognini, who had also beaten Haas in the last-eight at Stuttgart, will play third-seed Spaniard Nicolas Almagro, who beat fifth-seed Juan Monaco of Argentina 4-6, 6-0, 6-3 in just under two hours. (AFP)