The world number three from Spain came through 6-1, 7-6 (7/3) to stay on course for a gold medal to add to his four Grand Slam titles.
"I was very happy to get through in two sets. I played much better in the first set than I did in the second," he said.
"He raised his level and it was much closer."
Alcaraz, the reigning French Open and Wimbledon champion, needed to leave the court to have treatment on his right leg late in the second set and then had to save a set point.
"The leg isn't a problem, it's a tennis player's life, it's just a niggle."
The 21-year-old Alcaraz is also still in the men's doubles in Paris playing alongside Rafael Nadal.
In the next round of the singles he will face Roman Safiullin, the Russian player competing at the Olympics as a neutral.
