Marcos earned his first match win at the US Open in three years, advancing to the second round when opponent Facundo Bagnis retired due to injury at 6-4, 6-2, 1-1.
"It's tough to play out there," said Marcos after the match. "The conditions are so tough. It's a very noisy court. But I'm happy to get a win in a Grand Slam and play another match on Wednesday."
Marcos fired three aces and converted four of eight break points to move on after one hour and 29 minutes. He broke to open the match on his fifth opportunity and never looked back. Marcos will hope to equal his best result in New York with a win over 32nd seed Benoit Paire on Wednesday.
"I had an unfortunate injury that came at the worst time for me. It would have been nice to play in the Olympics and play again for my country. I had to deal with it and I'm happy it went away fast. The treatment from my doctors and my physio in Cyprus was great.
"I've played against Benoit Paire before and he likes playing in New York. It's going to be a very tough match. I just have to concentrate on what I have to do."
In three head-to-head encounters, Marcos' lone victory over Paire came in Rotterdam in 2013. They have since squared off at Roland Garros later that year, as well as in Tokyo in 2015.
