Pain-free Serena looks forward to Riske challenge

'She's a fighter on the court. She's playing really great, especially on the grass. She's attacking that ball really well. She doesn't let anything limit her'

Serena Williams reached her 14th Wimbledon quarter-final by overwhelming Spain's Carla Suarez Navarro 6-2, 6-2 even though she was not at her magnificent best on Court One on Monday.

The 37-year-old American, aiming for a record-equalling 24th Grand Slam title, produced 19 unforced errors, including a bizarre mistake when she leaned over the net to hit a volley and had the point docked.

"I should know the rules," Williams, who has been playing Grand Slam tennis for 21 years, said with a smile.

Williams also conjured 21 winners, some of which left the crowd gasping in admiration and her 30-year-old opponent helpless on the other side of the net.

She now faces Alison Riske, a former doubles partner, in the quarter-finals after the American upset Australian top seed Ashleigh Barty in three sets earlier on Monday.

Williams, seeded 11th, had little match practice coming into Wimbledon because of injury and teamed up with local hero Andy Murray in the mixed doubles to get some more playing time.

"I've had more matches this week than the past five months but it's definitely good and I know I can play and I'm now physically better," she said immediately after coming off court.

Later she added it felt good simply to be without pain.

"Doing three hours of treatment every practice , every match, just to be able to have 50% pain -- that was tough," she said.

"I can't tell you how much better I feel... that's a victory in itself."

Suarez Navarro, ranked 31 in the world and one of the smaller players on tour, lacks the big weapons and serving power needed for grass and has always had trouble against Williams.

Monday's defeat was her seventh against the seven times Wimbledon champion.

Though the Spaniard broke the American's serve in the second set, she had no answer for Williams's pounding groundstrokes. Suarez Navarro slipped trying to retrieve the ball to go match-point down, then mis-hit a backhand to concede defeat.

Williams, who first played at the All-England club as a 16-year-old in 1998, said she was still ambitious.

"I'm a really pumped player and of course I still want it or I wouldn't be here."

Williams knows all about her next opponent, 29-year-old Riske, having enjoyed playing doubles with the American.

"She's a fighter on the court. She's playing really great, especially on the grass. She's attacking that ball really well. She doesn't let anything limit her," said Williams.

"It was really fun to play doubles with her. We had a good time on the court. Also she was very serious, as was I...

"I think she's a great girl, a great person. She's just a great personality that you kind of gravitate to."