Cilic, who had just one victory this year going into the Ahoy stadium tournament, improved to a perfect 3-0 over Coric, whose career was sidelined last autumn by injury.

"It's always tough to play a countryman and Borna has been doing well in his comeback. It was not an easy match, even after winning the first set fast," said former US Open champion Cilic.

"Borna has proved himself as a 'next-gen' player. Maybe he didn't have the best season due to his knee surgery, but he's playing quite consistently."

Following his first-set thrashing, where he trailed 5-0, Coric steadied to square the match at a set each.

However, a break in the third by Cilic handed the top seed a crucial 4-3 lead.

Tomas Berdych, seeded fourth, hit 10 aces to defeat Frenchman Richard Gasquet 7-6 (7/4), 6-1 and advance into a contest against defending champion Martin Klizan of Slovakia.

Belgian third seed Dàvid Goffin earned a comeback win over Robin Haase, the last Dutchman in the field, 5-7, 6-4, 6-4.

"It's always nice to play these tournaments. They are smaller draws than Masters or Grand Slams, but the matches are always tough," said Goffin.