Nick Kyrgios booked a Japan Open quarter-final spot without having to take to the court after Radek Stepanek withdrew injured.

The Australian, seeded sixth in Tokyo, had an easy day at the office as his Czech opponent failed to overcome a back problem.

Kyrgios will now meet Gilles Muller, who was a 6-3 6-4 winner against Marcos Baghdatis.

Ivo Karlovic needed almost two hours to secure a straight-sets victory over Janko Tipsarevic as both sets went to a tie-break.

The Croatian held his nerve to prevail 7-6 (11-9) 7-6 (7-5) and set up a last-eight showdown with Gael Monfils.

Second seed Monfils enjoyed far more serene progress as he overcame French compatriot Gilles Simon 6-1 6-4.