There is just no stopping Juan Martin del Potro after the red-hot world number six overcame Milos Raonic in a thrilling quarter-final at the Miami Open.

Acapulco and Indian Wells champion Del Potro extended his winning streak to 15 matches courtesy of Wednesday's 5-7 7-6 (7-1) 7-6 (7-3) victory.

Argentine fifth seed Del Potro lost the opening set against the Canadian and looked out of it as he spoke to a trainer during the set break.

But the resilient Del Potro – seeking back-to-back-to-back trophies – rallied to outlast Raonic after almost three hours and consecutive tie-breaks in Miami midweek.

Del Potro, who celebrated his ATP-best 21st victory of the season, will contest back-to-back Masters 1000 semi-finals. Standing in the way of Del Potro and a third straight final is in-form American John Isner.

Isner was too good for Australian Open quarter-finalist Chung Hyeon, cruising to a 6-1 6-4 win in only 69 minutes at Crandon Park.

Seeking his maiden Masters crown, Isner – the 14th seed – won 97 per cent of his first serves to advance to his 11th ATP 1000 semi.

"This is actually the best I've moved all year," Isner said. "That's not working harder, or training harder off the court; that's just from me being more confident on the court."