Del Potro is in the hunt for a maiden Grand Slam title
Sixth seed Juan Martin del Potro came back from a set and a break down to beat Croatia's Marin Cilic and reach the US Open semi-finals.
Cilic, conqueror of Andy Murray in round four, made a fine start to his first Grand Slam quarter-final.
But Del Potro broke in game six of the second set and never looked back, coming through 4-6 6-3 6-2 6-1.
In his first US Open semi, Del Potro will face Rafael Nadal or Fernando Gonzalez, who meet later on Thursday.
And he will go into that match in buoyant mood after finishing so strongly against fellow 20-year-old Cilic.
The 16th seed from Zagreb got going in sensational fashion, breaking Del Potro in game five and, after serving out the first set, again at the start of the second.
But Del Potro, who initially seemed ill-at-ease with the cold conditions on Arthur Ashe Stadium, hit back to level at 3-3 and dominated from there on in.
Cilic completely lost his range as Del Potro broke at 4-3 before the Argentine served out the second set and then wrapped up the third in 36 minutes.
The fourth set was even more one-sided until Cilic offered late resistance with a break at 0-5 - but Del Potro responded immediately to seal his triumph in two hours and 32 minutes.