Williams screamed in pain as she was struck by cramp in her left leg at 6-5 down in the second set of her fourth round match with Daniela Hantuchova, but bravely carried on after treatment and managed to force a tie-break.
Hantuchova led 4-2 when the rain intervened, buying the two-time champion almost two precious hours to receive treatment.
And although Hantuchova won the tie-break when play resumed, Williams fought back with typical tenacity to win the decider and seal a 6-2 6-7 6-2 victory and a quarter-final clash with Justine Henin.
‘‘I never had an injury like this ever, ever,’’ Williams revealed afterwards. ‘‘I didn’t know what it was. When I went down I didn’t expect to be able to get up.
‘‘It’s definitely among my gutsiest matches. I had little to no movement. It was all about hanging in there, hitting aces and going for it.
‘‘I just decided at one point it was over and I was going to die trying, I was not going down to day — there’s no way. I figured my heart wouldn’t give out.’’
Meanwhile the elder Williams, Venus, survived another scare before beating Akiko Morigami to secure her place in the fourth round.
The American resumed 6-2 1-4 up and Morigami served for the match before Williams came through 6-2 3-6 7-5.
Williams, who struggled to beat unseeded teenager Alla Kudryavtseva in the first round, was in trouble again when Japan’s Morigami levelled at one set all and moved 5-3 up in the decider.
Three-time champion Williams broke back to love but had to save another two break points as the rain fell before finally clinching victory with a service winner.
Top seed Justine Henin demolished Patty Schnyder 6-2 6-2 to become the first woman to reach the quarter-finals.
Second seed Rafael Nadal squandered a match point against Robin Soderling but was 6-4 6-4 6-7 (7-9) 4-6 2-0 ahead when play was called off at 8.21pm.
Former champion Lleyton Hewitt was two sets to the good against Guillermo Canas, Novak Djokovic won the first set against Nicolas Kiefer and Mikhail Youzhny was two sets up against Jarkko Nieminen.
Marcos Baghdatis completed a surprisingly easy victory over David Nalbandian to book his place in the last 16 at Wimbledon.
Last year’s semi-finalist triumphed 6-2 7-5 6-0 in one hour 41 minutes in between Monday’s rain delays.
Elsewhere Tomas Berdych claimed a straight-sets win over Hyung-Taik Lee, of Korea, and Jonas Bjorkman won the battle of the golden oldies with Wayne Arthurs.