ROTTERDAM, Netherlands - Second-seeded Marin Cilic reached the World Tennis Tournament quarterfinals by defeating Gilles Muller of Luxembourg 7-6 (2), 7-6 (7) in the second round on Wednesday.

Neither player faced a break point in the first set, but Muller saved five in the second.

Cilic had two match points at 6-4 in the tiebreak, then saved a set point at 7-6 down as Muller fought back strongly.

"I was expecting a close match. Luckily, I was serving well and I was mentally focused," said Cilic, runner-up here to Tomas Berdych two years ago. "Gilles is a very difficult player to play against indoors, and I'm happy to be through."

The 2014 U.S. Open champion next plays Philipp Kohlschreiber, who won against qualifier Ivan Dodig of Croatia 6-4, 6-2.

The German proved clinical on Dodig's serve, converting four of five break-point chances, and solid on his own — winning 75 per cent of points on second serve.

Meanwhile, fifth-seeded Gael Monfils of France beat 19-year-old Borna Coric of Croatia 6-3, 5-7, 6-2 in a match littered with 22 break-point chances.

Monfils served for the match at 5-4 in the second set then lost three straight games.

He finally served out victory to set up a match against either countryman Gilles Simon, seeded third, or German teenager Alexander Zverev — who won their first-round matches on Wednesday.

In other first-round play, No. 8-seeded Viktor Troicki, Jeremy Chardy, and Roberto Bautista Agut also advanced.