Caroline Wozniacki through in straight sets in Madrid

Denmark's Caroline Wozniacki has advanced to the third round of the Madrid Open by defeating Germany's Mona Barthel in two tight sets.

The former world number one made just a single break in the opening set that was enough to seal a 6-4 success.

She again found a way through her opponent's serve in the next and had the chance to serve it out in the 10th game.

However, Barthel saved a match point and went on to break back and level the second at 5-5.

The game then went to a tie-break where Wozniacki didn't let her small blip games earlier affect her, racing to a 7-2 victory in the breaker.

Wozniacki, 21, will face world number nine Serena Williams after the American came through comfortably against Anastasia Pavlyuchenkova in another of this evening's matches.