Marcos turned in a strong performance to push 17th seed Lucas Pouille to four sets, but he would fall 6-7(4), 6-4, 6-4, 6-3 in the second round of the US Open.
Making his 13th appearance in New York, he earned a first-round victory over Mikhail Youzhny before succumbing to Pouille on Grandstand. Marcos fired 47 winners, including 23 aces, but was unable to overcome seven breaks of serve.
Playing aggressive tennis, Marcos would grab the opening set in a tie-break and surged to a 4-2 lead in the second set. But Pouille found his form, winning four straight games to draw level at a set apiece. After dropping the third set, he did well to break Pouille midway through the fourth, but would eventually fall after three hours and 18 minutes.
Marcos is projected to return to the Top 90 of the ATP Rankings with his second-round finish at Flushing Meadows. He was facing Pouille for the first time.