Switzerland's Belinda Bencic put friendship aside to beat Croatia's Donna Vekic and reach her first Grand Slam semi-final at the US Open.
The 13th seed, who knocked out defending champion Naomi Osaka in the previous round, won 7-6 (7-5) 6-3 against her good friend.
She will face Canadian Bianca Andreescu or Belgian Elise Mertens next.
The 22-year-old will now return to the top 10 of the world rankings for the first time in more than three years.
She reached a career-high seventh in February 2016 before injuries and wrist surgery left her as low as 328th.
"I dreamed of this like a little kid so now that I'm here I'm really enjoying it," said Bencic, who ended a five-year wait to improve on her previous best Grand Slam showing of a US Open quarter-final.
Bencic, who was knocked out of the French Open by Vekic in May, got the better of her hitting partner this time round in a match full of baseline rallies.
Vekic, 23, had her chance in the first set, where she broke in the ninth game but failed to serve it out, with it eventually going to a tie-break, which Bencic took charge of.
The Swiss broke twice in the second set, sealing victory on her third match point when Vekic hit a forehand wide.
The pair shared a warm embrace at the net and Bencic was confident their friendship would survive.
"We're both professional enough to be friends off the court and competitive on the court," Bencic said. "I think we did well. I'm sure off the court we are friends still."