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Munar served for the match at 6-5 in the decider, but the 38 year-old found a late surge to become the second-oldest man to reach the Round of 16 at ATP Masters 1000 level in series history (since 1990). Monfils is the oldest man to reach the fourth round in Miami tournament history.

“I've played so many matches and I know it’s not easy to close out matches with a big atmosphere,” said Monfils, who won 11 of the final 12 points. 

“If you win the first point, it’s key. I was fortunate enough to return down the line and come down to the net and I caught him. I knew at that moment, that point can be a game changer and it was. Crowd getting involved and then it’s pure experience and pure joy from my side as well.”

In front of a packed Butch Buchholz court, Monfils occasionally looked drained, only to rally back and outlast the Spaniard in long, gritty baseline exchanges. Monfils and Munar played a total of 214 points, with Monfils holding his nerve in key moments to advance.

Across the Frenchman’s three matches this week, he has spent six hours and 28 minutes on court.

Monfils, who earlier this year won his 13th tour-level title in Auckland, improved to 14-4 on the season. He will next face American Sebastian Korda, who the former No. 6 ousted just two weeks ago in Indian Wells. Monfils’s narrow 7-6(2), 7-6 win marked his first meeting with Korda.

In other action, fifth seed Casper Ruud advanced with a 6-4, 7-6(4) victory behind a dominant serving performance against 30th seed Alejandro Tabilo. The Norwegian dropped just five points behind his first delivery and fended off all three break points he faced. Ruud also struck 11 aces.

The 2022 finalist improved to 3-0 against Tabilo and will next face in-form Francisco Cerundolo, who defeated Tommy Paul 6-2 7-6 (6-4).

 Ruud, 26, recorded a 10th match win at an ATP Masters 1000 event for the third time in his career (13 in Rome, 10 in Monte-Carlo).