Belgium's Alexander Blockx continued his remarkable run at the Madrid Open, upsetting defending champion Casper Ruud 6-4, 6-4 on Thursday to secure his spot in the semi-finals of a Masters 1000 event for the first time in his career.

The unseeded Blockx, who had never won an ATP Tour-level match on clay before this month, will now face second seed Alexander Zverev, who comfortably dispatched Italian Flavio Cobolli 6-1, 6-4 in the other quarter-final match.

Blockx has been a revelation in Madrid, where he knocked out third seed Felix Auger-Aliassime en route to the last four. Thursday’s victory, which took just 96 minutes, was his latest milestone in what has been a breakthrough tournament for the 21-year-old. With this win, Blockx becomes the fourth-lowest-ranked player to reach the semi-finals in the history of the Madrid Open.

The world No. 69 was in fine form as he overpowered Ruud with aggressive baseline play and solid serving. Blockx showed few signs of nerves, despite the magnitude of the match, as he held his ground and took charge of the contest from the start.

"I'm proud of how I've played these past couple of matches," Blockx said in his on-court interview. "I think the conditions suit me well here. The clay is slow, so I have time to settle and go for my shots, but the altitude and heat make it quite fast at times. It's the perfect combination for me."

Meanwhile, Zverev delivered a clinical performance against Cobolli. From the first point, the German was dominant, taking advantage of the Italian’s unforced errors to race through the opening set. Zverev hit 12 aces, committed just two double faults, and won eight of 12 net points, finishing the match with 23 winners.

This victory for Zverev comes just weeks after Cobolli had knocked him out of the semi-finals at the Munich Open. However, the two-time Madrid champion was quick to dismiss any notion of revenge.

“No revenge, I love Fabio, he's one of my favourite guys on tour,” Zverev said. “This is sport; sport can change very, very quickly. I played an amazing first set, and he didn’t.”

The semi-final clash between Blockx and Zverev promises to be a thrilling encounter as both players continue their impressive runs in Madrid.

-Reporting by Karan Prashant Saxena in Bengaluru. Editing by Christian Radnedge and Clare Fallon/Reuters