Victoria Azarenka of Belarus celebrates her victory over Li Na of China.

Madrid – World No 1 Victoria Azarenka was made to battle hard for a semi-final place at the Madrid Open as she eventually overcame Roland Garros champion Li Na 3-6 6-3 6-3 on Friday.

The Belarussian, runner up in Madrid last year, looked to be cruising at 4-1 up in the third before China's Li broke back. Li was unable to take advantage of four break-point chances, however, and 36 unforced errors told its own story.

Azarenka will face newly-installed world No 3 Agnieszka Radwanska or American qualifier Varvara Lepchenko in the last four.

Former world number ones Serena Williams and second seed Maria Sharapova follow next on centre court. Fifth-seed Samantha Stosur takes on another qualifier Czech Republic's Lucie Hradecka in the other quarter-final. – Reuters