That game had a 40-15 lead for Schwartzman, a brilliant Nadal drop volley that rubbed out the second set point, a Nadal break point, a lovely duo of Schwartzman overheads for a third set point and, just then, after a first-serve fault, a spectator in the 15th row apparently fainting.
Nadal patted Marterer sympathetically on the chest at the net after winning on his second match point. Schwartzman saw two set points come and go but at the third time of asking, after a delay while a spectator was helped out after feeling ill, the Argentine ripped a forehand victor.
Once Nadal and Schwartzman do take to the court, we should be in for an exhibition of power-hitting from the greatest clay-courter of all time against a player who despite standing at just 5ft 7in packs a mighty punch from the baseline.
The Spaniard had been on course to do the same at this year's event but saw the first set against Schwartzman go the way of the Argentine, who claimed it 6-4.
Nadal's last win after losing the opening set came against Novak Djokovic in the 2014 final.
When Schwartzman broke in the third game of the second set, the alarm bells were ringing in the Nadal camp and although he quickly levelled he was immediately broken again.
The players were forced off the court for 40 minutes, but when they returned Nadal levelled for 3-3 and let out a trademark roar of "vamos".
That proved costly as Nadal broke and then repeated the trick to move into a 5-3, 30-15 lead.
Her semi-final with Halep will also decide the world number one spot next week.
Halep won in 59 minutes with the second set taking just 22 minutes.