DOHA — Top-seeded Carlos Alcaraz overcame Croatian veteran Marin Cilic 6-4, 6-4 Monday to reach the round of 16 at the Qatar Open.

Cilic, the 2014 U.S. Open champion who has fallen to No. 192 in the rankings, was playing his first match of the season after recovering from a long-term knee injury. The 36-year-old Croatian led 4-3 and 0-40 on Alcaraz’s serve in the second set, but the Spanish four-time major winner managed to recover and then broke in the next game.

“I am just really happy that I stayed calm at that moment, breathing, going through my routines, making good points,” Alcaraz said. “That’s why I was able to win in two sets.”

Alcaraz will play either Zhang Zhizhen of China or Italy’s Luca Nardi next.

Earlier, seventh-seeded Grigor Dimitrov lost 6-4, 6-4 to Jiri Lehecka.

Several other top players will play their first matches on Tuesday.

Second-seeded Alex de Minaur will face Roman Safiullin. Novak Djokovic, who had to pull out of his Australian Open semifinal with a hamstring injury, will take on Matteo Berrettini.

Daniil Medvedev, Andrey Rublev and Stefanos Tsitsipas will also play on Tuesday.