ATP Tour Rotterdam Open Semifinals Feature Surprise Dark Horse Advances

The ABN AMRO Open Rotterdam witnessed one of the most stunning upsets of the 2026 ATP season on Wednesday evening, as 24-year-old qualifier Adrian Kozlov from Serbia defeated world No. 8 Stefanos Tsitsipas in straight sets to reach his first ATP 500 semifinal.\n\nKozlov, ranked 127th in the world and playing on his first tour-level main draw wildcard, showcased incredible composure under pressure to secure a 6-4, 7-6(3) victory over the Greek star. The match lasted just over two hours, with Kozlov saving three break points in the decisive second set while maintaining his aggressive baseline game that has caught the tennis world's attention this week.\n\nThe Serbian qualifier's path to the semifinals has been nothing short of remarkable. After surviving three qualifying rounds last weekend, Kozlov has now defeated two Top 20 players in consecutive matches, following up his second-round victory over No. 15 seed Cameron Norrie with today's masterclass against Tsitsipas.\n\nTsitsipas, who was seeking his third Rotterdam title, struggled with unforced errors throughout the match, committing 31 compared to Kozlov's disciplined 18. The upset marks the biggest ranking differential victory for a qualifier at an ATP 500 event this season, with Kozlov earning 180 ranking points and €85,000 in prize money.\n\nKozlov will face defending champion Jannik Sinner in Friday's semifinal, setting up what promises to be another David versus Goliath encounter. The young Serbian's fearless approach and powerful forehand have drawn comparisons to his compatriot Novak Djokovic's early career breakthrough moments.\n\nWith this victory, Kozlov is projected to break into the top 80 of the ATP rankings for the first time, marking a career-high achievement that validates years of hard work on the Challenger circuit. His success in Rotterdam has already earned him wildcards into next month's Indian Wells and Miami Masters events, potentially launching what could be a breakout 2026 season.