Spanish second seed Rafael Nadal responded to the challenge thrown down by 2014 champion Marin Cilic as he battled to reach the US Open quarter-finals with a four-set win.
Nadal, 33, ultimately had too much quality for the Croatian 22nd seed in a 6-3 3-6 6-1 6-2 victory in New York.
Cilic, 30, briefly rediscovered his best form to level before wilting.
Nadal, the 18-time Grand Slam champion, will play Argentine 20th seed Diego Schwartzman in the last eight.
After defending champion Novak Djokovic retired injured from his last-16 match against Stan Wawrinka on Sunday, Nadal is considered the joint favourite for the men's title alongside Swiss great Roger Federer.