Former champ del Potro eases into US Open quarter-finals

Argentina's Juan Martin del Potro celebrates on the way to a US Open fourth-round victory over Borna Coric

Former champion Juan Martin del Potro cruised into the quarter-finals of the US Open on Sunday with a 6-4, 6-3, 6-1 victory over Croatia's Borna Coric.

The third-seeded Argentine, who lifted the trophy in Flushing Meadows in 2009, is in the quarter-finals for a third straight year and sixth time overall, reaching the last eight without dropping a set.

Del Potro broke Coric in the final game of the opening set, and from there he was in control in a match again played to the accompaniment of cheers and chants from a group of del Potro's friends who made the trip from Tandil to watch him.

Coric, the 21-year-old 20th seed, sought treatment for a right thigh problem late in the second set and never threatened in the third.

Del Potro wrapped it up after two hours and five minutes with his sixth service break of the match when Coric smacked a forehand into the net.

"After winning the first set I started to play much better," said del Potro. "I saw Borna with some problem for movement toward the end of the match and I focused on my game.

I played even better than the last match," added del Potro, who has spent an average of just two hours and 11 minutes per match on court.

Del Potro will take on American John Isner for a semi-final berth.

Isner, seeded 11th, defeated Canadian Milos Raonic in a battle of big-servers 3-6, 6-3, 6-4, 3-6, 6-2.

Del Potro has won seven of 11 prior matches with Isner, including a straight-sets victory in the fourth round of the French Open this year.