After an easy first week at the U.S. Open, Rafael Nadal figures to have a challenge in the fourth round.

The No. 2 seed faces No. 22 Marin Cilic in a matchup of past champions, with the winner getting a spot in the quarterfinals.

Nadal has played just two matches and spent a little more than four hours on the court, getting a walkover in the second round and winning twice in straight sets.

Cilic, the 2014 champion, hopes to improve to 6-0 in fourth-round matches at Flushing Meadows.

Top-ranked Naomi Osaka is also in action, while American teenagers Coco Gauff and Caty McNally try to remain unbeaten in doubles. Taylor Townsend and Kristie Ahn of the U.S. hope to extend their longest runs in Grand Slam tournaments.