Former US Open champions Marin Cilic and Juan Martin del Potro powered into the fourth round of the Miami Open on Sunday with straight-sets victories.

Argentina’s fifth-seeded del Potro, chasing his second ATP Masters title in as many weeks, breezed past Japan’s Kei Nishikori 6-2, 6-2.

Ranked sixth in the world after vanquishing Swiss great Roger Federer in the final at Indian Wells last weekend, del Potro needed just 73 minutes to book a fourth-round meeting with Filip Krajinovic of Serbia, who beat France’s Benoit Paire 6-3, 6-3.

Second-seeded Cilic also reached the fourth round with a 7-5, 7-6 (7/4) victory over Canadian Vasek Pospisil.

Cilic produced six aces and saved all three break points he faced. But Pospisil made him work to finish it off, save three match points on his own serve in the 12th game of the second set.

“It was a relief at the end,” Cilic admitted. “I had those three match points at 6-5 and there was that great rally at deuce. I was playing really well in the tie-break, returning really well and serving really good. I saved the best for last and I’m really pleased with the victory.”

Cilic will face 14th-seeded American John Isner for a quarter-final berth. Isner defeated Russian veteran Mikhail Youzhny 6-4, 6-3.

Cilic and del Potro are the biggest names left in a field lacking star power thanks to the early exits of Federer and Novak Djokovic and the injury absences of Rafael Nadal and Andy Murray.

Third-seeded Grigor Dimitrov of Bulgaria joined the exodus as he fell 6-4, 6-4 to unseeded Frenchman Jeremy Chardy.

Del Potro, the hottest player on the ATP tour right now, is actually in search of a third straight ATP crown after back-to-back victories in Acapulco and Indian Wells.

His win in the California desert was his first in a Masters 1000 event, a welcome milestone after a succession of injury setbacks almost forced him into retirement in 2015.

“I think I’m playing good,” Del Potro said after his 13th straight match win. “I can play even better, but I need to get confidence playing in this court, trying to keep winning matches.

“But it’s not easy,” he added. “My body starts to feel tight because of all my success.”

In other third-round action, South Korean Chung Hyeon posted a convincing 6-1, 6-1 victory over American qualifier Michael Mmoh.

Chung, who has yet to drop a set in Miami, needed just 63 minutes to advance to a meeting with Portugal’s Joao Sousa, who rallied for a 1-6, 6-3, 6-4 win over American Jared Donaldson.