Others - including United States former tennis great Billie Jean King and ex-male professional James Blake - praised Nadal's victory, which was dominant despite an injury scare with hand cramp in the latter stages of the third set.
Federer returned from a five-year Grand Slam drought to beat Nadal in last year's Australian Open final, then won an eighth Wimbledon and retained the Australian title in January, beating Marin Cilic in the final on both occasions.
Nadal's victory on Sunday meant that all past six Grand Slam titles have been won by either Federer or himself.
However, he said: "I've had long and mentally tough clay-court season because I played nearly all the matches possible after coming from an injury".
"So coming back and have the chance to win in Monte Carlo, Barcelona, Rome, and now especially here, yeah, it's very emotional for me". But I guess the way he's been playing the last three sets yesterday (Thursday, vs Schwartzman) and the last two sets today (Friday, vs del Potro) is going to help give him confidence.
On another day, if the result had been different in 1968, it might have been Laver in Paris presenting Nadal with the trophy.
Nadal won the first two sets.
But it ultimately proved a futile mission as, just like in all but two of Nadal's previous 87 matches here, the incredible Spaniard proved invincible, winning 6-4, 6-3, 6-2.
There was still fight in Thiem, though, and he had a break point when Nadal served at 4-2 - a game in which the Spaniard was warned for taking too long to serve.
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Thiem dug in - especially in the roughly 13-minute sixth game - but he crumbled attempting to stay in the set, making four unforced errors.
Thiem save three break points to hold his service into the third set, but the "King of Clay" responded by fully exhibiting his powerful forehand for astute winners. He pounded huge serves, topping 135 miles per hour (220 kph) about 25 miles per hour (40 kph) more than Nadal's fastest - and that translated into seven aces, but also five double-faults.
That it was not was testimony to Nadal's level, which never wavered, despite everything Thiem threw at him.
Seemingly cruising to victory, that's when Nadal called for the trainer. Nadal appeared to take more tablets. Frustrated ThiemNadal, however, turned the screw in the 10th game and Thiem seemed to grow nervous, sending a forehand long to hand his opponent the opening set. For the last 14 years, he hasn't relented.
The victory also allowed the 32-year-old Nadal to hold onto the No. 1 ranking, just ahead of Federer.
"When someone wins 11 times here, for me it's unbelievable to think about this", said uncle Toni.
Only Nadal, Pete Sampras and Ken Rosewall have managed the feat of winning Grand Slam titles in their teens, 20s and 30s.