Gauff, who secured her place with two wins this week, lost to Viktoria Azarenka 7-6 (2), 4-6, 6-3.
The 33-year-old Azarenka, from Belarus, reached her first semifinal since last October, when she advanced to the final at Indian Wells.
“She’s a young player, but she’s had quite a few already experiences on the tour. I love watching Coco play,” Azarenka said. “I believe that she’s going to do great things in the sport. I feel like she just needs a little bit more to kind of take that one step forward.”
Azarenka, a former No. 1-ranked player in the world, will face off against third-seeded Jessica Pegula, who cruised to a 6-2, 6-2 win over former U.S. Open Champion Sloane Stephens.
With the win, Pegula has 37 victories in WTA 1000 tournaments, the most since 2021. She broke a tie with Swiatek (36).