David Goffin defeated Marin Cilic 7-6 (7-4), 6-2 on Thursday to reach his first career Masters 1000 semi-final with the victory at Indian Wells.
Goffin, the Belgian 15th seed, was the first between the pair to advance this far in the elite ATP series.
2014 US Open winner Cilic became the second straight grand slam champion victim for Goffin, who put out French Open holder Stan Wawrinka in the previous round.
"I knew that my level was there," Goffin said.
"I knew I had to stay focussed on what I had to do - to play in a big stadium against Marin, a player who I beat two weeks ago in Davis Cup. I was really confident, and I was focussed on my plan and not thinking about the semi-final."
The win in just under an hour and three-quarters was the second for Goffin over Cilic, who wore a large strapping on his right knee but insisting it was more precautionary than therapeutic.
Gofin saved four set points in the 12th game of the opening set, taking it into a winning tiebreaker.
Cilic stands 12-8 in a so-so season, while Goffin improved to 12-4. Cilic had ended an 11-match losing streak against top 10 players as he beat Frenchman Richard Gasquet in the fourth round.
But the Croatian still stands at 0-8 in Masters 1000 quarter-finals.
"I knew that against Marin it's gonna be a battle of serves," Goffin said.
"I knew that on my serve I had to battle to win every service game, because sometimes he can serve bombs and in 10 seconds can win his games. I had to be focused on my service games. At the end I stayed focused in the tiebreak. It was the key of the match to win the first set and be more relaxed in the second to play much better."
In a later match, Canadian Milos Raonic was facing Gael Monfils in the bottom half of the draw at the Tennis Garden.
In the women's quarters, Czech Karolina Pliskova beat promising Russian teenaged newcomer Daria Kasatkina 6-3, 6-2 and will next play the winner from 13th seed Victoria Azarenka and Slovak Magdalena Rybarikova.
"I was really happy with the way I played the singles. It was one of the best matches that I've played here so far," Pliskova said. "I played some good tennis this week, so I have chances to go and improve the ranking and get close to top 10 again."