Angelique Kerber and Roberta Vinci were among the top seeds to ease into the last eight of the WTA Nurnberger Versicherungscup.

Second-seed Kerber, on home soil at this International clay-court event in Nuremberg, cruised through her first set against Klara Koukalova and then showed her battling qualities to seal a 6-1 7-6 (7-2) victory.

After breaking her opponent at every opportunity in the opening set, world number 11 Kerber found herself 5-1 down in the second as Koukalova looked destined to force a decider.

But Kerber rescued six set points in managing to bring the set back on serve, before dominating the tie-break as Koukalova's chance slipped away.

Fourth seed Vinci, meanwhile, needed just 50 minutes to dispatch Tereza Smitkova 6-2 6-1 and set up a quarter-final tie with Kurumi Nara - seeded seventh - after the Japanese overcame Stefanie Voegele 6-3 6-4.

Karin Knapp, ranked sixth at this event, saw off Anna-Lena Friedsam 6-1 6-3 to book her place, while Kerber will meet Misaki Doi in the last eight after the world number 112 came from a set down to defeat Zhang Shuai 1-6 6-3 6-1.