*** Information provided by the Associated Press

RIO DE JANEIRO -- Venus Williams isn't used to taking the court in doubles uncertain whether she can win.

That's why the four-time gold medalist sat in her changeover chair after an Olympic semifinal victory Saturday with her face in her hands and her jaw dropped in stunned elation.

"With Serena, I expect to win -- I've got to be honest," she said of her younger sister, with whom she won three of those golds.

But in the only draw in which she's still in contention in Rio de Janeiro, Venus' mixed doubles partner is someone with whom she had never played before: American teammate Rajeev Ram.

"We had no idea how we were going to play together," she said, "so the emotion is almost even bigger because ... you don't know what to expect. It's a wild feeling."

The 36-year-old Williams couldn't stop jumping up and down after she and Ram rallied for a 2-6, 6-2, 10-3 tiebreak victory over Sania Mirza and Rohan Bopanna of India. She's guaranteed a record-tying medal and will play Sunday for gold -- and more milestones -- in the final.

"To feel what I feel with Serena with someone else, I never thought that would happen," she said.

"I could double for Serena," Ram joked.

The champions will be Americans: Williams and Ram face the other U.S. team, Bethanie Mattek-Sands and Jack Sock.

Williams' fifth medal will match the most in Olympic history. Kathleen McKane won five (one gold) in the 1920s. With a victory Sunday, Williams would become the first five-time Olympic tennis gold medalist, moving one ahead of her sister in that category. It would also make her the first player to win gold in singles, doubles and mixed doubles.

The Williams sisters have always treasured the opportunity to go to the Olympics, where Venus was the singles champion in 2000 and Serena in 2012. They were undefeated in doubles together through their first three Olympic tournaments, but everything seemed to go wrong this time around.