Veteran Ivo Karlovic has taken three sets to beat 18-year-old Mikael Ymer of Sweden in the second round of the Stockholm Open.

Ymer, who upset Fernando Verdasco in the first round for his first ATP tour victory, thrilled the home crowd by winning the first set but ultimately couldn’t match the power of his Croatian opponent.

Karlovic hit 16 aces to win 4-6 6-4 6-4 in 1 hour, 47 minutes.

Alexander Zverev of Germany is also through to the quarter-finals after beating Frenchman Adrian Mannarino 7-5 6-4.

In first-round action, last year’s Stockholm Open finalist Jack Sock of the United States beat Malek Jaziri of Tunisia 3-6 6-3 7-6 (7-5).

Argentina’s Juan Martin del Potro and Jurgen Zopp of Estonia also advanced to the second round.