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The Spaniard, looking to equal Roger Federer's record of 20 Grand Slam men's singles titles, is used to slow starts at Roland Garros and this year's debut on Monday was no different.
On the revamped court Philippe Chatrier, whose roof stayed open throughout, Nadal converted all of his five break points to set up a meeting with American Mackenzie McDonald.
The second seed, who had complained about the new balls being too heavy, did not appear too bothered in front of some 200 fans, wrapping up the match with a service winner.
"It's a different Roland Garros. Of course we play in the same place. But the conditions are completely different than any other Roland Garros that we've played," said Nadal.
The French Open was moved from its usual May-June spot to September 27-October 11 amid the Covid-19 crisis, meaning players have to deal with rough weather conditions - colder, more humid.
Nadal arrived in Paris with no title on clay under his belt after being beaten by Argentine Diego Schwartzmann in the quarter-finals of the Italian Open, but Monday's match gave him reasons to be optimistic.
With the Spaniard's topspin having less of a devastating effect on the heavier clay, Nadal had to adapt and play more aggressively than usual, taking the ball earlier to unsettle his opponent - a tactic that worked perfectly.
He broke in the fifth game as he bagged the opening set in solid fashion, and he stole his opponent's serve again in the third game of the second.
With a mountain to climb after falling two sets behind and as blue skies ate away the dark clouds, Gerasimov broke for 2-0 in the third set.
Nadal quickly regained control, however, and levelled for 2-2, with Gerasimov twisting his ankle on the last point of the fourth game.
The physiotherapist taped the Belarusian's ankle and play resumed after a short interruption with Nadal breaking again for 3-2.
Gerasimov's challenge was fading as Nadal piled on the pressure to seal a routine win, moving a step closer to a potential semi-final with last year's runner-up, Austrian third seed Dominic Thiem.
In other matches, US Open winner Thiem defeated Croatia's Marin Cilic 6-4 6-3 6-3.
Thiem, seeded third, has lost to Nadal in the last two men's finals on the Parisian clay. The pair are in the same half of the draw and could meet in the semi-finals.
Fourth seed Daniil Medvedev, however, was knocked out in the opening round for a fourth straight year at Roland Garros, with Hungarian Marton Fucsovics taking a 6-4 7-6(3) 2-6 6-1 victory.
In a French Open epic, Italian qualifier Lorenzo Giustino recovered from an opening set bagel to edge out local favourite Corentin Moutet 0-6 7-6(7) 7-6(3) 2-6 18-16.
The match, which began on Sunday, was the second-longest encounter in the tournament's history, falling 28 minutes short of the 2004 first round epic when Fabrice Santoro beat French compatriot Arnaud Clement in six hours 33 minutes.
SERENA THROUGH FIRST ROUND
In the women's draw, Serena Williams resumed her hunt for a record-equalling 24th major title with a 7-6(2) 6-0 win over fellow American Kristie Ahn.
Newly-crowned Strasbourg champion Elina Svitolina continued her impressive run on clay with a 7-6(2) 6-4 win over Russian Varvara Gracheva.
Former champion Garbine Muguruza said there was no such thing as a relaxing match these days after narrowly avoiding a first-round exit at the French Open when she battled for three hours to beat Slovenia's Tamara Zidansek 7-5 4-6 8-6.