STUTTGART, Germany -- Top-ranked Iga Swiatek ended US Open champion Emma Raducanu's first clay tournament run with a 6-4, 6-4 win Friday to move into the Stuttgart Open semifinals.
Swiatek extended her win streak to 21 matches and moved closer to what would be a fourth consecutive title after victories in Doha, Indian Wells and Miami.
The quarterfinal was much closer than their only previous encounter at any level, a 6-0, 6-1 win for Swiatek at 2018 Junior Wimbledon, but Raducanu's lack of experience on clay still told against the former French Open champion.
Swiatek immediately broke Raducanu and held serve with ease to take a first set in which Raducanu won just three return points. Raducanu improved markedly in the second set -- despite needing a medical timeout after an examination of her lower back and hip at 2-1 down -- and made Swiatek work hard.
Raducanu was in her first career WTA tournament on clay after playing on the surface for the first time at senior level last week for Britain against the Czech Republic in the Billie Jean King Cup. The clay-court swing was already over last year when Raducanu burst onto the scene with a charge to the fourth round on the grass of Wimbledon.
Friday's contest was the 19-year-old British player's first match against an opponent ranked in the world's top 10, as she aimed to win three matches at the same tournament for the first time since her surprising US Open title.
Swiatek goes on to face Liudmila Samsonova in the semifinals after the Russian won 7-5, 6-3 against home favorite Laura Siegemund of Germany.
Paula Badosa and Aryna Sabalenka will meet in the other semifinal.
Badosa outlasted Ons Jabeur 7-6 (9), 1-6, 6-3 to reach the last four after having lost in the quarterfinals at her last two tournaments in Miami and Charleston.
Sabalenka ended a seven-month wait for a tour semifinal since last year's US Open, the Belarusian hitting 10 aces as she beat Anett Kontaveit 6-4, 3-6, 6-1.