Eighth seed Casper Ruud battled past teenager Holger Rune 6-1, 4-6, 7-6(2), 6-3 on Wednesday to reach the French Open semi-finals and become the first Norwegian to reach this stage in any Grand Slam.
He will play Croatian 20th seed Marin Cilic in the semi-final.
"Of course a lot of nerves all day to get going. It's tough to find calm and peace," Ruud said. "I started great but Holger fought back and raised his level."
"I had played him three times already, now fourth, I guess I know a little bit how he plays. He plays fearless, goes for big shots."
"It's a big day for Norwegian tennis," Ruud said. "I will use tomorrow to prepare. These matches are the ones you are dreaming about playing."
The 23-year-old quickly raced to a 5-0 lead, twice breaking the teenager in the process and blitzing him with sensational cross-court forehand winners, clinching the first set after 34 minutes.
In his first French Open appearance, Rune, who had dumped out fourth seed and last year's finalist Stefanos Tsitsipas in the previous round, was left shaking his head at his opponent's faultless performance, looking towards his box for advice as his unforced errors started to accumulate.
Rune, who had lost all three previous encounters to Ruud in straight sets, quickly changed tactics, playing three consecutive drop shots while also charging to the net to move 1-0 up.
The world number eight continued to keep him pinned to the back and got another break to move into the driving seat with a 3-2 lead.
The Dane, however, was in no mood to give up just yet, battling back from 0-40 on Ruud's serve to break when he chased down a drop shot and whipped a forehand past his opponent to level.
Some cracks started to appear in the Norwegian's game and Rune pounced, winning the second set on his first opportunity on Ruud's serve.
Neither refused to budge in the third until both were broken once but Ruud powered through the tiebreak to go 2-1 up.
Rune saved two break points on his serve to level at 1-1 at the start of the fourth but Ruud kept up the pressure.
He got the break he wanted when Rune sent a crosscourt forehand wide, to go 5-3 up and served for the match before winning it with a disputed line call.
Marin Cilic completed his set of Grand Slam semi-finals by knocking out No.7 seed Andrey Rublev 5-7, 6-3, 6-4, 3-6, 7-6(10/2) in a marathon showdown on Wednesday at Roland-Garros.
Cilic, a US Open champion in 2014 and a former runner-up at the Australian Open and Wimbledon, had never made it past the quarters in Paris but has now made the semis or better at all four majors.
The 33-year-old Cilic now awaits the winner of tonight's showdown between No.8 seed Casper Ruud and Danish teenager Holger Rune.
Rublev clinched a 57-minute opening set before Cilic raced to take the next two. The world No.7 fought hard to force a decider, in which he saved a match point when serving at 4-5.
Rublev had a chance to break for 6-5 but some clutch serving from Cilic got the Croatian out of trouble as he held for 6-5 in an eight-minute game. The match fittingly went to a deciding tiebreak, which Cilic valiantly snatched to punch his ticket to the last four.
Rublev has now lost all five Grand Slam quarter-finals he has reached so far in his career.
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