Thiem stayed with Nadal in the early going on a cloudy and steamy afternoon; the temperature was 77 degrees (24 Celsius), the humidity approached 70 per cent.
In 11 finals in Paris, Nadal has only lost six sets as he matched the all-time record of most singles titles won at the same Grand Slam event set by Margaret Court at the Australian Open during the 1960s and 70s.
But at 4-5 Thiem's serve let him down badly, handing Nadal three set points.
Nadal celebrated in relatively low key fashion, but then there is not much novelty value in this. He saved two of a mere three break points. Thiem withstood a barrage of break points to hold in a marathon sixth game, which he thought he had won at 40-30 when he left a wide ball, only for the umpire to overrule the line judge. So there was mild concern when Nadal called for the trainer midway through a game, requiring treatment on what looked like cramp in his hand. But against an opponent of Nadal's caliber, a lack of variance in his game plan proved crippling. Nadal had another massage at 5-2 and he ended Thiem's ordeal on his fifth match point when the Austrian returned long.
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But against Thiem, there was nothing wrong with Nadal's start.
The top-seeded Nadal enters Sunday with a 10-0 record in title matches at Roland Garros and an overall career mark of 85-2 at the clay-court Grand Slam tournament.
Dominic Thiem couldn't get near the veteran on the day, despite the fact the Austrian had been the only player to defeat Nadal on Clay during this current season.
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Nadal's Barcelona Open semifinal win over David Goffin was his 400th tour-level clay-court match win, making him the fourth man in the Open Era to win 400 matches on clay, after Vilas (659), Manuel Orantes (502) and Muster (422).
The forecast says there is a chance of rain.
That was swatted away with Nadal's double-handed backhand, though, and the second set duly went the way of the favourite.
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