London: Seven-time champion Serena Williams reached her 12th Wimbledon semi-final yesterday with a hard fought 6-4, 4-6, 6-3 victory over unseeded American compatriot Alison Riske yesterday.

Serena, 37, who is two wins away from equalling Margaret Court's Grand Slam singles title record haul of 24, looked far from convincing as Riske pushed her the whole way over an engrossing two-hour duel.

"It was really satisfying," said Williams, whose clay court season was affected by a knee injury. "I wouldn't have won that match a couple of weeks ago. I'm glad that I was able to come through. She beat so many great players. She was really so close to taking the win today."