World number one Carlos Alcaraz says he was “scared” after injuring his ankle during his first-round victory at the Japan Open in Tokyo on Thursday.

Top seed Alcaraz twisted his left ankle against Argentina’s Sebastian Baez with the first set level at 2-2 and had to receive treatment from the physio and heavy strapping.

He returned to the court and broke Baez to lead 5-4, but his team seemed to signal for him to stop at this point, before play was then suspended for rain causing another delay.

When Alcaraz, who won the men’s US Open title earlier this month, and Baez re-emerged under the roof, the Spaniard dominated the rest of the contest and won 6-4 6-2.

“I was scared too, I’m not going to lie,” said six-time Grand Slam winner Alcaraz.

“When I landed on the ankle, I was worried to be honest because it didn’t feel good at the beginning. I’m just happy that I was able to play after that and play such good tennis. Let’s see.

“I think it’s not going to be easy the next day and a half for me. I will try to recover, to do whatever it takes to be ready for the next round.”

Alcaraz faces Belgian Zizou Bergs in the second round on Saturday.