The Wimbledon champion brushed aside Alexander Shevchenko 6-2 6-1 on the outdoor clay inside the Caja Magica in his first match in nearly a month in Madrid on Friday.
Alcaraz was coming off a right arm injury that kept him from playing in Monte Carlo and Barcelona, and had feared he might not be able to play this week.
"I didn't know how I would feel on the court, and I had my doubts," Alcaraz said.
"I had started practice this week taking things very easy and slowly picking up the intensity, and I still had doubts swimming in my mind. But today there was none of that. I surprised even myself and I am happy with how good I felt."
This was Alcaraz's first match since losing to Grigor Dimitrov in the Miami Open quarter-finals nearly one month ago.
Madrid is the Spaniard's first appearance on the European clay-court swing — he struggled in Buenos Aires and Rio de Janeiro in February — as he aims to win his first French Open title next month.
The Spaniard said that he would be happy to play "three of four matches" at the ATP 1000 tournament.
Alcaraz, who had a first-round bye, played with a wrapping covering most of his right arm from his wrist up past his elbow.
But he looked pretty much like the same aggressive player who has dominated here for the past two years and given Spanish tennis fans hope that there is life after Rafael Nadal.
Alcaraz broke Shevchenko's serve four times and will next face Thiago Seyboth Wild after the Brazliian beat Lorenzo Musetti 6-4 6-4.
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