Sport's most enduring sibling rivalry will be played out on US Independence Day after Venus Williams exacted brutal revenge and Serena Williams displayed raw desire to inflict a double defeat on Russia at Wimbledon.

The American sisters will be setting off fireworks on women's final day for the second year running at the All England Club, but on Thursday Serena came within a heartbeat of missing out on the Fourth of July celebrations.

At 4-5, 30-40 down in the deciding set, Serena was staring defeat head on as Elena Dementieva stood one point away from reaching her first Wimbledon final.

Instead, a split second's hesitation by the Russian allowed Serena to hit a wobbly backhand volley off the tape and the American snatched her get-out-of-jail free card to crawl over the finishing line with a 6-7 7-5 8-6 win over the fourth seed.

Clocking in at two hours and 50 minutes it was the longest women's semi-final match at Wimbledon since records started being kept in 1969.

"It's definitely one of my more dramatic victories. I felt like I was down pretty much the whole match. To come out on top was, you know, a great feeling. I wanted to win really bad," Serena told reporters.

While little sister Serena had to fight tooth-and-nail to survive a match that showed off everything that is good about women's tennis, Venus proved that there is still a gulf between her and the rest of the women's field at Wimbledon when she walloped clueless top seed Dinara Safina 6-1 6-0.

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