Serena Williams: 'I had to remain focused'

Serena Williams has revealed that keeping her focus after dropping the first set was key to her victory over Garbine Muguruza in the Australian Open fourth round.

The world number one looked to be heading for a shock exit before fighting back to win in three sets, but the American was keen to praise her opponent, who she had lost to at Roland Garros in 2014.

The 33-year-old said: "Congratulations to Garbine, she played so well and she did everything that she needed to do in the first set.

"I didn't start slow but she played really well and I just had to try to stay focused."

Williams will now play Dominika Cibulkova in the next round after the Slovakian hitter defeated Victoria Azarenka in three sets.