Danish teenager Holger Rune upset top-seeded Alexander Zverev 6-3, 6-2 Wednesday to reach the quarterfinals of the BMW Open tennis tournament.

The 18-year-old broke Zverev's first service game in each set to take control of the match on his way to his first career win over a player ranked in the top 10. Zverev is ranked No. 3.

"I have a lot of respect for him, and I obviously didn't expect to win in two sets, and with a score like this," Rune said. "But it was a really hard match; we played a lot of rallies, and I'm really happy about my performance today."

It was the first time since 2014 that Zverev, a two-time winner of the tournament, lost his opening match on the Munich clay courts.

The German player has yet to win a title this year after winning six last year, including the Olympic gold medal. Rune is ranked 70th and had not won back-to-back matches in the main draw of any ATP Tour event this season until now.

Rune next faces Finland's Emil Ruusuvuori, who won 6-3, 6-3 against Maxime Cressy.

Fourth-seeded Nikoloz Basilashvili needed nearly two hours to beat Ilya Ivashka 3-6, 6-2, 6-4 and set up a quarterfinal with seventh-seeded Miomir Kecmanovic. Cristian Garin lost an all-Chilean first-round match 6-3, 6-4 against Alejandro Tabilo, and Botic van de Zandschulp beat Brandon Nakashima 7-6 (3), 6-3.