Monfils finished off Cilic in five minutes after their match was interrupted by heavy rain Wednesday night.

Next up for Monfils is No. 6 seed Diego Schwartzman. The Frenchman said waiting to play the decisive points against Cilic was very hard.

"We only played four points, but I had to keep my concentration all day long. I am so glad I could do that," Monfils said.

Cilic won only one match on the clay in Rio in his first tournament since he reached the Australian Open final in January.

No. 2 seed Dominic Thiem moved on to the next round when Spain's Pablo Andujar retired due to injury in the seventh game of their match.

Thiem, who won the Rio Open last year, will face Spain's Fernando Verdasco in the quarters. Verdasco beat Argentina's Nicolas Kicker 6-7 (3), 6-2, 6-0.

Fourth-seeded Fabio Fognini also advanced with a 4-6, 6-4, 7-6 (6) victory against American Tennys Sandgren.

The Italian will face Slovenian Aljaz Bedene, who eliminated No. 3 seed Pablo Carreno Busta of Spain with a 6-2, 5-7, 6-2 win.

Carreno Busta lost last year's final against Thiem.