Serena insists she'll get better

Serena Williams has warned her rivals that she will only get better after struggling to overcome Zie Zheng on Saturday.

The 30-year-old had looked comfortable during the first week at Wimbledon as she brushed past Barbora Zahlavova Strycova and Melinda Czink, but lost the first set against her Chinese opponent in a tie-break. However, she then went on to play some of the best tennis of the opening week before finally overcoming her opponent 9-7 in the decider to set-up a fourth round clash with Kazakhstan's Yaroslava Shvedova. Williams has now warned her rivals that, following her scare, she is determined to step up a level as she looks to win her fifth SW19 singles title. "I have to make sure I do better," Williams said. "Usually I return well but I hit so many errors off my returns against Zheng. "I was just off against her, although she played unbelievable. I still think I can play better."