Still it was an improvement from 12 months ago when Murray was stretched to five sets in the first two rounds, which likely took a toll in the final he lost to Novak Djokovic.
Former British number one Greg Rusedski, commentating on the match for Eurosport, believes Murray will need to improve to beat Del Potro.
Murray has the better of the pair's head-to-head record, with his six wins from nine matches including a memorable Rio 2016 Olympics final success. On Thursday, Martín del Potro climbed over the net to console his opponent, Nicolás Almagro, who was visibly upset by an injury that forced him to withdraw from their match. He is starting to play very well for periods of a match and now seeks to add the consistency required.
"They don't like it when we behave badly - which is good!"
The pair only met twice past year but they were two matches that will live long in the memory.
Will this be another classic? "It was tough" said Del Potro.
It's absolutely crucial that Murray must keep his intensity. Yes Martin Klizan is unsafe but Andy just didn't have that consistency.
The match was tied at a set all and 1-1 in the third when Almagro quit playing, keeping his hands on his knees and head bent before breaking down to the court and weeping badly.
He was offered a lifeline early in the fourth thanks to a wayward Murray forehand and made it through to 5-3, only to fail once again when trying to serve out the set. I've got to keep taking the initiative to bully players with it when I can.
The South American is no stranger to the hardships of injury himself, having suffered a string of ailments which have stalled his career in recent years.
Delpo is still a great competitor and he understands how to play on clay.
"I think the surprise of knowing what you are going to have on that special day you give birth is prob the best surprise you can ever have!" He's taken little steps in that direction, but has then backtracked from time to time. "I did not grow up with brothers, only sisters and we all say "she" more than "he"'".
It could well be, yeah. "I think I was feeling very confident, so I was dictating a lot with my backhand and forehand". "Juan Martin plays better than his ranking".
It's going to probably be a tight five sets maybe.
They know each other's games really well, and they've known each other since they were juniors.
Czech second seed Karolina Pliskova and third-seeded Simona Halep of Romania, both firm women's title favourites after the first round exit of world number one Angelique Kerber, look for places in the last-32.
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