Seven-time Gerry Weber Open winner Roger Federer was rarely troubled in his quarter-final victory over Florian Mayer as he edged closer to defending his title in Halle.

Top seed Federer is far and away the tournament's most successful competitor and showed why during Friday's 6-0 7-6 (7-1) success over home favourite Mayer.

The Swiss world number two has now won all six of his career meetings against Mayer and said: "I thought I played very well today".

Mayer had no answer to Federer in a one-sided first set, but showed character to put up a much stronger fight in the second - only to then be beaten easily in a tie-break.

Federer will face Ivo Karlovic in the semi-finals after the Croatian blew away Tomas Berdych with 45 aces in a 7-5 6-7 (8-10) 6-3 victory.

Karlovic bettered his own existing record for aces in a three-set match by one as the veteran recorded his second top-10 scalp of 2015 following victory over Novak Djokovic in January.

The other semi-final will see second seed Kei Nishikori take on Andreas Seppi.

Nishikori came through a testing encounter against Poland's Jerzy Janowicz 6-4 5-7 6-3, while Seppi was the beneficiary of Gael Monfils' retirement.

The Italian - who knocked out Tommy Robredo in the previous round - was 6-1 1-0 to the good when fourth seed Monfils was forced to retire after crashing into the side boards.

The Frenchman appeared to injure his hip and will be eager to make a swift recovery ahead of Wimbledon, which gets under way later this month.