Williams, bidding for a sixth Wimbledon title and a calendar Grand Slam, was on the brink of a dramatic third-round exit when Watson served for the match at 5-4 in the final set. But Serena, who had trailed 3-0 in the decider, showed why she has won 20 Grand Slam titles as she broke back before finally sealing an epic escape in two hours and 14 minutes in front of an enthralled 15,000-strong crowd on Centre Court.

Serena's 53 winners and 13 aces were just enough overcome her 33 unforced errors in the match of the tournament to date.

"I've had some tough losses but that was probably my toughest match, playing Heather in front of her home crowd," Williams said. "She played unbelievable and really I think she should have won the match.

"She was up two breaks and she just really gave her all and showed us what a great player she is."

The 33-year-old American will face 16th seed Venus on Monday for the first time in a Grand Slam since beating her in the 2009 Wimbledon final. The sisters' last meeting came in 2014 when Venus won in Montreal, but Serena holds a 14-11 advantage over the 35-year-old in their career head to head.

They have clashed five times previously at Wimbledon, with Serena winning three times and Venus twice.

"Venus is in better form than I am, so I think she has a little bit of an advantage going into that match. But at least one of us will be in the quarter-finals, so that will be good," Serena added.

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