Marcos is on a roll at the Antalya Open, advancing to the quarter-finals at the ATP World Tour 250 event.
Marcos survived a tight encounter against Carlos Berlocq 6-4, 3-6, 7-5 in two hours and 20 minutes. Into his first quarter-final since Auckland in January, he fired seven aces and claimed a dominant 89 percent of points on his first serve.
Marcos secured three of 11 break chances, including the first of the match at 3-all in the opening set. Despite dropping the second set, he rebounded nicely in the decider, breaking for the match in the 12th game. He emerged with the victory after firing a forehand at the net that Berlocq was unable to return.
Marcos will feature in the last eight at the inaugural tournament in the coastal Turkish city of Antalya. He will be the favourite against qualifier and 222nd-ranked Ramkumar Ramanthan, who upset top seed Dominic Thiem on Tuesday. It is their first head-to-head meeting.
Marcos is looking to reach his an ATP World Tour semi-final on grass for the third consecutive year. He was a semi-finalist in Nottingham in 2015 as well as in Newport in 2016.