Serena entered the match with a 15-11 head-to-head advantage over Venus but the high number of losses to her 35-year-old sibling represented the most posted by any opponent against the world number one, who knew she was in for a tough fight.
The 33-year-old top seed, winner of 21 grand slam singles titles, took charge of the opening set by securing service breaks in the fifth and seventh games of a match that felt like a heavyweight title bout after a brilliant start by Venus.
However, Venus looked more like the player who has claimed seven grand slam singles titles in the second set, unleashing her power and drawing groundstroke errors from Serena for two service breaks that sent the match to a third set.
Serena seized control early in the decider and rode the momentum to the finish in her quest to join Maureen Connolly (1953), Margaret Court (1970) and Steffi Graf (1988) as the only women to win Wimbledon and the Australian, French and U.S. Opens in the same season.
The sisters exchanged a warm hug at the end of the 98-minute battle and Serena was asked about their embrace in the middle of the massive Arthur Ashe Stadium court in an on-court interview.
“It’s a really great moment,” Serena said. “She’s the toughest player I ever played in my life and the best person I know.
“So it’s going against your best friend and at the same time going against the greatest competitor for me in women’s tennis, so it was really difficult today.”
Serena, who belted 12 aces and unleashed 14 winners off her blistering two-handed backhand, said once the match started, she forgot about sibling connections.
“When I’m playing her, I don’t think of her as my sister, because she’s playing so well, hitting big serves and running a lot of balls down,” Serena said.
“When you’re in the moment you don’t really think about it. We trained all our lives to be on this court…”
Before Serena was able to take control of the opening set, she had to contend with a barrage of huge serves and forehands from her big sister. The three-times defending U.S. Open champion said it needed a mighty effort to hang on for the win.
“Holding serve in the third set was all I could do. She came out hitting so hard, just blasting every shot. I was on defence a lot,” she said of her 23rd-ranked sister.
“This is a big moment for both Venus and I,” she added. “We both have a chance to be in the semi-finals and it’s a grand slam so we both want to do the best that we can.”
Next up for Serena will be unseeded Italian Roberta Vinci, who earlier defeated France’s Kristina Mladenovic 6-3 5-7 6-4.