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Opelka's serve was the key to his success as he fired 24 aces past the Russian favourite to win in two tiebreak sets 7-6 (7-5) 7-6 (7-5) and reach the semi-finals.

Medvedev led the second-set tiebreak 4-1, but coughed up three untimely double faults in his next three service points to bow out.

“It’s been a good serving week, especially today,” Opelka said.

“When it’s hot like this, the court starts to bounce a lot more and react more to the different spins on my serve. Medvedev has been one of the best players in the world the past five years, so to get through him is a great win.

“His double faults at the end were because of my serve. The pressure that I put on him after serving so well and consistently is what caused the three double faults at the end of the tie-break.”

Opelka is the second lucky loser to advance to the to the semi-finals at ‘s-Hertogenbosch after Australia's Rinky Hijikata in 2023.

The American will next face Zizou Bergs for a spot in the final after the Belgian beat Mark Lajal 7-6 (7-2), 7-6 (7-4) in their clash to advance.

Medvedev will lose his top 10 ranking on Monday after this defeat, with Ben Shelton taking his spot courtesy of a 6-4 6-4 win over Jiri Lehecka at the Stuttgart Open quarter-finals.

In the other half of the draw at ‘s-Hertogenbosch, Gabriel Diallo forced another upset by beating No.3 seed Karen Khachanov 7-6 (8-6) 6-4 to reach his second ATP Tour semi-final.

Diallo hadn't won on grass on the ATP Tour until this week, but is in good form in 2025, saving two match points to defeat Khachanov, racking up 19 aces during on the way to the last four.

His next test will be against No.2 seed Ugo Humbert, beat Nuno Borges 6-1 6-4 in little more than an hour to take his spot in the semi-finals.