Djokovic leads their epic head-to-head rivalry 26-25.
5-7 win over Frenchman Gilles Simon after fading light interrupted their last-16 clash the previous evening with the fifth seed up two sets to one.
Roger Federer after his loss to Kevin Anderson: "I couldn't feel very well off the baseline".
"I think it was great quality tennis and in the final set there were some awesome points", said 2008 and 2010 champion Nadal.
"Sorry to Juan Martin, he's an unbelievable opponent and player". In some ways he deserves to win as well.
The timing of this one - a match that's decider was described by Andy Murray in the BBC commentary box as "one of the best sets of tennis I have ever seen live" - was somewhat unfortunate as it clashed with England's World Cup semi-final.
"At least I could hit my forehand in or out, but is not a good way to close the match like that".
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"I will try to hold my service games most of the time".
"(Djokovic) is one of the toughest opponents.
Del Potro trailed 1-3 but at 5-5 he fired down a swinging ace to reach match point number five and this time Simon cracked, netting a backhand to the relief of the Argetine who roared his approval. I don't know if it was the breeze or just a bad day from my side.
Del Potro raised his game again, though, claiming his third tie-break success of the match to book his date with Nadal.
One of those was on double fault in the tiebreak and the giant Argentine pounced to level the tie.
A couple of slips from the fifth seed gave Nadal a sniff and after the Spaniard broke for a 3-2 lead in the fourth, Del Potro thumped a ball at full pelt into the turf in frustration. A tired Del Potro, a semi-finalist in 2013, finished with 33 aces and 77 winners but even those impressive statistics were not enough.