World number one Serena Williams survived an almighty scare at Wimbledon, battling back to beat inspired Briton Heather Watson in three sets and stay on course for a 21st grand slam title.

Williams, who has lifted this year's Australian and French Open crowns, was forced to dig deep in front of a raucous home crowd after an error-strewn showing against the superb Watson, recovering from 3-0 down in the final set to win 6-2 4-6 7-5.

The 33-year-old will face her sister Venus in the last 16 - their 26th career meeting - as she continues her bid for a sixth Wimbledon crown.

"I have had some tough losses but that was probably my toughest match. I think she played unbelievable and should have won the match," the American told reporters.

"She could get beyond the top 20, she is playing really well... She was playing so good there was nothing I could do."

Williams has now won 24 grand slam matches in a row but will hope for more consistency in the fourth round.

Earlier, Maria Sharapova eased past Romanian Irina-Camelia Begu 6-4 6-3.

Barring a brief wobble in the second set when the Russian was broken serving for the match at 5-1, it was a straightforward day at the office for Sharapova, who knows what it takes to lift the trophy having claimed the title in 2004.

"There is only one champion in the end and the one who raises their game is the champion," she said.

Sharapova led 5-1 in the second set before the mini wobble [Getty Images]

Results:

1-Serena Williams (U.S.) beat Heather Watson (Britain) 6-2 4-6 7-5
16-Venus Williams (U.S.) beat Aleksandra Krunic (Serbia) 6-3 6-2
Zarina Diyas (Kazakhstan) beat 14-Andrea Petkovic (Germany) 7-5 6-4
23-Victoria Azarenka (Belarus) beat Kristina Mladenovic (France) 6-4 6-4
6-Lucie Safarova (Czech Republic) beat Sloane Stephens (U.S.) 3-6 6-3 6-1
4-Maria Sharapova (Russia) beat 29-Irina Begu (Romania) 6-4 6-3
30-Belinda Bencic (Switzerland) beat Bethanie Mattek-Sands (U.S.) 7-5 7-5
CoCo Vandeweghe (U.S.) beat 22-Samantha Stosur (Australia) 6-2 6-0

Source: Reuters