Young gun Borna Coric upset Kevin Anderson 2-6 6-4 7-6 (7-3) to reach the semi-finals of the BNP Paribas Open in Indian Wells on Thursday.
The Croatian recorded his first win in four attempts against the South African, who reached the US Open final last year and is back into the top 10 of the world rankings.
The upset victory in the California desert means the 21-year-old will play in his first Masters 1000 semi-final against the winner of the clash between world No 1 Roger Federer or Hyeon Chung of South Korea.
"It was very tough," Coric told Sky Sports. "In the first set I couldn't find my rhythm because he was playing way too fast and I wasn't serving too good. But then I just decided to relax and fight.
"I'm not playing tomorrow so I get a day off. I will practice about one hour and just chill."
Coric initially looked out-gunned by the big-serving Anderson, but after weathering an onslaught of huge serves in the first set, a scrappy Coric was able to force longer rallies in the second and third, where his speed and accuracy allowed him to control points.
The match appeared all but over when a frustrated Coric double faulted to hand Anderson a break for the 4-2 lead in the decisive third set but the world No 49 broke straight back and went on to force a tie-breaker.
Anderson played a mistake-riddled breaker and Coric pumped his fist in triumph after the seventh seed sent a forehand long to hand the Croatian a huge win.