Venus Williams exults after defeating Elena Dementieva in the semi-finals at Wimbledon on Thursday. (Reuters)

Wimbledon: Venus and Serena Williams won in straight sets Thursday to set up their third all-sister Wimbledon final and seventh Grand Slam championship matchup.

Defending champion and four-time winner Venus beat Elena Dementieva 6-1, 7-6 (3), then two-time champ Serena overcame two rain delays and served 14 aces to down China’s Zheng Jie 6-2, 7-6 (5).

It will be the first all-Williams final since 2003, when Serena beat her older sister in the championship match for the second year in a row. Serena holds an 8-7 career edge over Venus, including 5-1 in Grand Slam finals. Since Venus won the US Open in 2001, Serena has won five straight of their major finals.

“She’s a tough opponent,” Serena said. “I think she’ll be the toughest person I’ve played. I’m excited.”

“It’s every Williams for themselves,” Venus said.

Venus overpowered the fifth-seeded Dementieva in the first set and then prevailed in an error-filled tie-breaker to improve her record to 7-0 in semi-finals at the All England Club.

“I am dying for Serena Williams to get through,” said the 28-year-old Venus, who hasn’t dropped a set in five matches and will be going for her seventh Grand Slam title.

Venus then went back out to watch her 26-year-old sister, who sat through rain breaks in both sets before cranking up her big serve, saving a set point in the second set and finishing off the 133rd-ranked Zheng to put her one win away from an ninth Grand Slam crown.

After Zheng dumped a second serve into the net on match point, Serena looked more relieved than anything to get through the match. Venus fiddled with her fingernails as she watched alongside their father, Richard, in the players’ box.

“She definitely pushed me,” Serena said of Zheng, the first Chinese player to reach a Grand Slam semi-final and first wild-card entrant to get this far at Wimbledon.

“Unbelievable, and not only that she played a great game. She played like she had nothing to lose and she didn’t.

“I wanted to do more than make a Wimbledon final,” she added.

“I’m just happy to be back in a Grand Slam final.”

In men’s play, 32-year-old Rainer Schuettler outlasted Arnaud Clement 6-3, 5-7, 7-6 (6), 6-7 (7), 8-6 in a match that took two days to complete.

The German saved a match point at 5-4 in the fifth set before pulling out a 5 hour, 12 minute victory that sends him into the semi-finals against No. 2 Rafael Nadal.