Nadal was shown to be human on the surface when he lost to Dominic Thiem in straight sets at the Madrid Masters last month, ending a run of 50 consecutive sets won on clay.
Dabrowski's mixed doubles opener against Pauline Parmentier and Gregoire Barrere was stopped Friday with the French duo trailing 1-4 after taking the opening set.
But the head-to-head history is overwhelmingly in Williams' favor: She has won 19 of 21 meetings, including 18 in a row.
The Argentinian became the unlikely darling of Roland Garros after driving for 10 hours from Barcelona to Paris, with his brother, mother and gran, on Sunday in order to register in time as a lucky loser.
Royg had reached the fourth round at Roland Garros previous year.
Spain's Rafael Nadal, right, hugs France's Richard Gasquet after their third round match of the French Open tennis tournament at the Roland Garros stadium, Saturday, June 2, 2018 in Paris. It was nearly as if she'd never left the scene.
Del Potro had eight aces and broke his Spanish opponent's serve six times on Court Philippe Chatrier, taking just 29 minutes to win the third set.
Two-time French Open champion Maria Sharapova of Russian Federation has been pushed to three sets in her return to the Paris Grand Slam following a two-year absence.
Among others advancing were No 6 seed Kevin Anderson and No 9 John Isner.
Williams beat 70th-ranked Kristyna Pliskova of the Czech Republic 7-6 (4), 6-4 to reach the second round.
There was another upset as unseeded Ukrainian Lesia Tsurenko defeated 19th-seeded Slovak Magdalena Rybarikova 6-2, 6-4.
Gasquet actually won their last encounter - but it was at the Kooyong Classic exhibition event this year.
He will next face 11th seed Diego Schwartzman after the diminutive Argentine underlined his clay court capability with a 7-5 6-3 6-3 victory against the unseeded Borna Coric. And No. 1 seed Simona Halep starts her French Open campaign against 83rd-ranked Alison Riske of the United States. Their match was suspended for rain late Friday.
He will next play seventh seed Dominic Thiem, a 6-2 6-0 5-7 6-4 victor over Japan's Kei Nishikori.