Ross and Klineman took down Taliqua Clancy and Mariafe Artacho del Solar 21-15 and 21-16 to take gold.
The match lasted 43 minutes.
Ross, 39, of California, already had a bronze medal from the 2016 Olympics and a silver from the 2012 Olympics.
Neither were with Klineman, 31, also of California.
“I’m still trying to process it but I’m so in the present moment here with this team and this medal. I’m so proud of my other ones but just how this worked out, and the risks that Alix took to come out onto the beach and all her hard work … it doesn’t happen without that,” Ross told reporters after the game.
“I can’t fathom that it worked out the way it did. It’s kind of a fairytale story like, ‘oh, I’m going at 39 to try and get my gold medal’, and the fact that it actually happened feels so special and surreal. I’m just so proud of our team and so grateful for everyone who helps us get here,” she added.
Klineman was an indoor volleyball player before switching to beach volleyball and teaming up with Ross in 2017.
She won a gold medal in her first Olympics.
“People should realize what a risk April took taking me on as a partner,” Klineman said after the win. “When we joined together I had less than a year of experience on the beach and was not playing at a high level. She took my indoor experiences into account, and my goals and motivation. I think she felt how badly I wanted this. She saw something in me that no one else did. I’m so grateful that she was looking at my potential and took that bet on me.”
The silver that Clancy and Artacho del Solar took is the first medal for Australia since 2000.
Anouk Verge-Depre and Joana Heidrich won the bronze medal match for Switzerland.
Also on Friday, the U.S. women’s indoor volleyball team advanced to the gold medal game by beating Serbia in three sets.
They’ll face the winner of Brazil and South Korea.