Serena Williams is now two wins away from completing an historic calendar year Grand Slam.

She kept her bid alive by outslugging older sister Venus 6-2, 1-6, 6-3 in a power-packed, 98-minute quarterfinal at the U.S. Open on Tuesday.

When it ended, they met at the net for a hug, with a smiling Venus wrapping both arms around Serena at the massive Arthur Ashe Stadium.

“She’s the toughest person I’ve ever played in my life and the best person I know,” Serena said afterward in an on-court interview.

“It’s going against your best friend and, at the same time, going against the greatest competitor for me in women’s tennis.”

Next up for Serena will be unseeded Italian Roberta Vinci in a semifinal match Thursday, Sept. 9. Vinci earlier defeated France’s Kristina Mladenovic 6-3, 5-7, 6-4.

“She’s the favorite. Maybe she’ll feel the pressure,” Vinci said. “It all depends on her. If she serves well, she’s tough to return.

“But I have nothing to lose.”

Serena entered Tuesday’s match with a 15-11, head-to-head advantage over Venus. But Serena’s high number of losses to her 35-year-old sibling represented the most posted by any opponent against Serena, who is ranked as the world’s No. 1 player. She knew she was in for a tough fight.

Well-known people, such as Donald Trump — who was booed when shown on video screens — Oprah Winfrey and Kim Kardashian dotted the teeming stands, and the action under the lights in Arthur Ashe Stadium often was of high quality.

The 33-year-old Serena, 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.

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-time defending U.S. Open champion said she 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 defense a lot,” she said of Venus, who is ranked 23rd.

“This is a big moment for both Venus and I,” she added. “We both have a chance to be in the semifinals, and it’s a grand slam so we both want to do the best that we can.”