USA's Serena Williams reacts during her match against Russia's Anastasia Pavlyuchenkova at the 2016 Wimbledon Championships in London, Britain, July 5, 2016. [Photo/Agencies]

LONDON - Serena Williams battered Anastasia Pavlyuchenkova 6-4 6-4 at Wimbledon on Tuesday to join sister Venus in the semi-finals and said she was surprised and delighted the pair were still competing at the top of their sport.

The defending champion, seeking an elusive 22nd grand slam to equal Steffi Graf's open-era record, showed no sign of slowing down against 25-year-old Russian Pavlyuchenkova as they exchanged explosive groundstrokes.

Although Venus, 36, and Serena, 34, are the oldest women in the women's singles, the latter said they did not discuss retirement. They would know when the time came.

"I'm surprised at the longevity of it. That definitely took me by surprise," Serena said after the sisters also completed a 6-4 6-3 doubles victory over Czech pair Andrea Hlavackova and Lucie Hradecka following their singles matches.