Marcos blasted into the third round of the BNP Paribas Open in Indian Wells, defeating 14th seed Diego Schwartzman 7-5, 6-4 on Sunday.
Needing one hour and 36 minutes to prevail, Marcos' fighting spirit was on full display on Stadium 4. He would race to a double-break lead at 3-0 in the first set, only to see Schwartzman fight back and draw level at 3-all. But Marcos stayed the course and would claim the decisive break in the 11th game. A similar scenario played out in the second set, with Schwartzman battling back for 4-all. Marcos would break right back in the next game and immediately served out the match.
Marcos scored his biggest win thus far in 2018 over World No. 18 Schwartzman. It was his first victory over a Top 20 opponent since 2016, when he upset No. 8 Tomas Berdych in Halle. Argentina's Schwartzman was in strong form, having recently lifted the trophy at the ATP World Tour 500 event in Rio de Janeiro.
Marcos has won four matches in six days after coming through qualifying and defeating Yoshihito Nishioka and Schwartzman in the main draw. He is making his ninth appearance at the prestigious Masters 1000 event in Indian Wells, with his best result coming in 2006 (quarterfinals).
Marcos, who is projected to return to the Top 100 of the ATP Rankings in one week, faces lucky loser Dudi Sela in the third round on Tuesday. It will be their fourth encounter, with Marcos holding a 2-1 advantage. He most recently fell to the Israeli at the Surbiton Challenger last year, after scoring wins in Delray Beach in 2009 and Newport in 2016.