Canadian Bianca Andreescu became the first teen US Open semi-finalist in a decade, rallying to defeat Belgium's Elise Mertens on Wednesday and advance to a Last-4 matchup with Belinda Bencic. Andreescu, 19, from suburban Toronto, downed 25th seed Mertens 3-6, 6-2, 6-3 to book a Thursday clash against fellow Slam semi-final debutante Bencic, the Swiss 13th seed who beat Croatian 23rd seed Donna Vekic 7-6 (7/5), 6-3.

"I'm honestly speechless," Andreescu said. "I need someone to pinch me right now. Is this real life?" Either Bencic or Andreescu, who have never played each other, will reach her first Slam final on Saturday at Arthur Ashe Stadium, where first-time Slam winners have been crowned three of the past four years.