Australian Open 2012: day nine - in pictures

The first quarter-final of the day is Agnieszka Radwanska against Victoria Azarenka in which the No8 seed outplayed the No3 seed to take the first set on a tie-break 7-6 Photograph: Clive Brunskill/Getty Images

However Azarenka put that behind her and found her groove to take the next set 6-0 Photograph: Jason O'Brien/Action Images

She then took the third set 6-2 to make it through to the semi-finals. Despite serving six double-faults and throwing in 38 unforced errors, she showed maturing mental resolve by holding her nerve on the big points. Afterwards she said: "I'm really happy with my win. I think it was very important to see how I could adjust after not playing really well in the first set. I completely turned it around." Photograph: Cameron Spencer/Getty Images

The next quarter-final sees the No1 seed Caroline Wozniacki take on defending champion Kim Clijsters, with Wozniacki needing to win the match to keep hold of her world No1 ranking. There's a nervous start by both players with three service breaks in the first three games. Photograph: Toby Melville/Reuters

Clijsters held her serve in the next game and then went on to dominate the match, winning the first set 6-3 and then serving for the match at 5-2 in the second set Photograph: Cameron Spencer/Getty Images

However she let her guard down and allowed Wozniacki back into the match. Wozniacki took her chances and got back on level terms, going into the tiebreaker with momentum Photograph: Clive Brunskill/Getty Images

Clijsters, who had never lost any of her eight previous tiebreakers at Melbourne Park, hit a backhand down the line to take a 5-4 lead. She set up double match point with a crosscourt forehand winner... Photograph: Joe Castro/EPA

A volley gave her a 6-3, 7-6 victory and a place in the semi-finals. After the match she said: "It definitely didn't feel like being up a set and 5-2. I had to work really hard for it. Caroline is a great fighter ... I was happy to get through, and not in a three-setter because it's so hot." Photograph: How Hwee Young/EPA

The first men's quarter-final sees Roger Federer take on Juan Martín del Potro in their first meeting in a major since Federer lost to Del Potro in the 2009 US Open final. However from early on it was obvious Federer, who is chasing a 17th grand slam crown, was in no mood to let this happen again and raced into a 3-0 lead Photograph: Jason O'Brien/Action Images

Del Potro wasn't going to let Federer have it all his own way and with a titanic effort battled back to level it at 4-4 Photograph: Vivek Prakash/AFP/Getty Images

But serving at 4-5, Del Potro faltered as two wonderful forehand winners from Federer handed him two set points and he clinched it on the first as the Argentinian double-faulted under the pressure Photograph: Robert Prezioso/Getty Images

Federer gained the upper hand in the second set to take a 3-1 lead Photograph: Nicolas Asfouri/AFP/Getty Images

Again Del Potro came back and put up some stiff resistance at 5-3 but Federer eventually took the game and the second set Photograph: Cameron Spencer/Getty Images

From two sets down, a Del Potro comeback never looked likely. Federer broke twice to motor through the third set and sealed the match with an imperious backhand winner Photograph: Ryan Pierse/Getty Images

Tomas Berdych took on Rafael Nadal in the other men's quarter-final. The Czech player took the first set on tie-break, 7-6 Photograph: Andrew Brownbill/AP

Rafael Nadal disputes a line call with the umpire as the second set also goes to tie-break, although this time it is the spaniard who wins it 7-6 Photograph: Clive Brunskill/Getty Images

The momentum of the match swung in his direction as he also took the third set 6-4 Photograph: Nicolas Asfouri/AFP/Getty Images

Nadal continues to dominate the fourth set with some sublime tennis and leads 5-3... Photograph: Joe Castro/EPA

...before breaking Berdych to nil to win the match 6-7, 7-6, 6-4, 6-3 and head into the semi-finals where he will meet Roger Federer Photograph: Vivek Prakash/Reuters