Petra Kvitova has stormed into the semi-finals at the Brisbane International with a straight sets victory over America's Jennifer Brady.

No 5 seed Kvitova held serve throughout and gained momentum during the match, speeding to a a 6-4, 6-2 win to set up a mouth-watering semi-final with Madison Keys who defeated fellow American Danielle Collins 6-4, 6-1.

Meanwhile, Australian Open champion Naomi Osaka was forced to fight for her place in the final four by Kiki Bertens in a two-hour battle. Osaka's performance was far from her best but she managed to hang on and claim the win 6-3, 3-6, 6-3. 

She will face highest remaining seed Karolína Plíšková in the semi-final after the Czech produced a convincing performance to overcome America's Alison Riske in straight sets 7-6 (8), 6-3

The semi-finals will both take place on Saturday January 11 when all players will vye for a place in the final on Sunday.