Top-seeded Marin Cilic needed a comeback to beat Benoit Paire 5-7, 6-3, 6-2 on Tuesday in the second day of the ABN Amro World Tennis Tournament in Rotterdam, Netherlands.
The 28-year-old Cilic smoked 13 aces in a two-hour challenge from the Frenchman Paire.
Cilic will face fellow Croatian Borna Coric, who defeated Karen Khachanov 7-6(6), 7-6(10), in the second round.
"It was definitely a tough match. I expected a tough one," Cilic said. "He's an extremely talented player. With his style of play, you never know what's coming. It's good for me that I'm winning these kinds of matches. Especially now that I've had a few losses this season."
In other matches, sixth-seeded Jo-Wilfried Tsonga topped Stefanos Tsitsipas 6-4, 7-6(2) in 89 minutes and Philipp Kohlschreiber upset eighth-seeded Lucas Pouille 7-5, 6-2.
"Even though I lost my serve (at the end), I played well," the 31-year-old Tsonga said. "I'm pretty happy with how I played today and hopefully I will get better every day.
"It was difficult, as I did not know him at all. That's unusual on the Tour, never seeing somebody at all. I didn't know where to play at the start or what to expect."
Tsonga will face 33-year-old Gilles Muller in the second round.
"He is a very good player, Tsonga said of Muller. "It's a good challenge for me in the second round and I will hope to play good tennis. He has been playing well since the start of the year, playing his best tennis ever. It will be a serious match for me."
Kohlschreiber will face Martin Klizan, who beat Fernando Verdasco, in the second round.