Serena and Sharapova move into Key Biscayne quarters

Serena Williams produced 20 aces and blasted her way into the quarter-finals of the Sony Ericsson Open with a 7-5, 6-3 win over Australian Samantha Stosur on Monday.

It was not all plain sailing for Williams, who lost her first service game of the match but came back to grind out the set in the first meeting between the two players since Stosur beat the American in the 2011 U.S. Open final.

Down 5-2 in the second, Stosur twice saved match point and forced Williams to serve out for the match and although the American trailed 0-40 she booked her spot in the last eight.

"I think for the most part things are working pretty decent," said Williams, who said 'revenge' for her defeat at Flushing Meadows had not entered her head.

"I honestly feel like I can do better but my serve was hot and that is pretty cool," she added.

Russian Maria Sharapova also sealed a place in the quarters with a 6-4, 7-6 win over compatriot Ekaterina Makarova despite being broken four times.

Makarova fought particularly hard in the second set but eventually fell 7-3 in the tiebreak.

"She had opportunities and served for the second set but I just hung in there and stayed consistent. I played a much smarter tiebreak," she said.

Sharapova was hampered by a worrying 11 double-faults but said she wasn't overly concerned yet.

"It not easy to play with that but I managed to win the game in two sets, so that's a plus," she said.

Sharapova, the runner-up here last year, will face China's Li Na after she beat German Sabine Lisicki 3-6, 6-4, 6-2.

Later on Monday, Venus Williams faces Ana Ivanovic.