Laura Robson
Laura Robson loses in straight sets to Kaia Kanepi in the fourth round at Wimbledon. [Reuters]

Laura Robson crashed out of Wimbledon in the fourth round after losing in straight sets to Estonian Kaia Kanepi, while world number one and defending champion Serena Williams was knocked out by Sabine Lisicki.

Williams had looked as though she would make it through to the quarter-finals after racing into a 3-1 lead in the third set but it was Lisicki who caused the upset as she remained positive and eventually secured a 6-2 1-6 6-4.

Meanwhile British number one Robson had opportunities in the first set of her match but was unable to convert as she eventually succumbed to a 7-6 (8-6) 7-5 loss in one hour and 35 minutes.

Kanepi struggled with injuries last year but has showed her quality to force her way back up the rankings and it was her big hitting that eventually proved simply too much for the 19 year old to handle.

"I am very very happy," declared Kanepi. "It was very tough match and I am happy to get through. My serve went well and I played a very good baseline match today."

Robson was the huge crowd favourite on centre court and quickly got into her stride as she earned a break point on Kanepi's second service game. But some good serving and a missed forehand from the Brit meant that the Estonian took the lead.

However, Robson was in control of her service games and quickly earned three more break points with the scores level at 4-4. A huge whipped forehand into the corner would seal the break and the young Brit would serve for the set.

The pressure clearly got to Robson though as a double fault and a wild forehand would mean we were back on serve. Comfortable holds from both players would follow as the first set headed towards a tie-break.

Robson raced 5-2 ahead but once again she looked nervous on her own serve and the score was soon levelled at 6-6. A crunching forehand winner from Kanepi set up set point and then another error from the Brit handed the first set to her 28 year old opponent.

The world number 46 was now looking confident and serving well. At 3-3 she earned two break points but Robson would twice save them with huge aces before managing to hold under massive pressure.

Robson was beginning to make some unforced errors on her forehand and with the scores level at 5-5 she was broken to love.

Kanepi would have four match points saved by the teenager but she finally converted her chance with another huge winner and she will now play Lisicki in the quarter-finals.

Sabine Lisicki
Sabine Lisicki celebrates after beating Serena Williams. [Reuters]

The 23 year old took the first set in impressive fashion but Williams responded superbly to dominate the second and then race into a 40-15 lead at 3-1 in the final set.

Williams was the odds on favourite to retain her title but Lisicki fought back and simply kept going for winners as she eventually secured one of the biggest victories of her career.

"I am still shaking, I am so happy," Lisicki told the BBC. "Serena played a fantastic match, she is such a tough opponent. It is an amazing feeling to win this match. This is such a special place for me and the crowd were brilliant to me. I gave it everything I had, I fought for every single point to try to win it somehow. I'm not thinking about the next match yet."