At one point Nadal, the reigning champion and 10 times victor, found himself a set and a break down to the diminutive Argentinian Schwartzman.
The Spaniard saw his 37-set winning streak at Roland Garros come to an end against the Argentine on Thursday before improving his level after a rain interval, only for a second interruption to end the day's play, with Nadal serving for the second set.
Nadal was back on serve immediately when the exuberant underdog put too much on a groundstroke, but Schwartzman regained the advantage with a simple volley to lead 4-3 after toying with the Spaniard.
Breaks were swapped twice in the first set before 25-year-old Schwartzman broke the Nadal serve for a third time to lead 5-4.
Schwartzman also missed three break points before his brief revival was ended when Nadal took his fourth match point to win in three hours and 36 minutes.
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A rescued break point in the opening game of the third was further evidence of Marterer's fortitude and Nadal was guilty of losing focus, smashing a routine forehand into the tramlines to go 3-1 down.
They will return on Thursday morning.
Play continued though, with the set following a similar pattern to the first, as Nadal broke back before dropping his serve to 15.
"To have had the victories that I have had, to have the results that I have, obviously moving a step in the right direction", said the five-time Grand Slam champion who had made the last-eight in Madrid and semis in Rome in the run-up to Paris.