A frequent - and gleeful - villain at the tournament he won in 2021, Medvedev crashed out in the opening round in 2025 but was all business this time around with 34 winners against just 11 from his opponent on Sunday (Monday AEST).
"You need to play your game - I knew he was going to do some drop shots, some underarm serves," Medvedev said. "I needed to make some winners, put some pressure on him."
Gaston's creative shot-making had little impact on the nimble-footed, six-foot six-inch Medvedev, and the Frenchman did himself no favours as he handed his opponent the break with a misplaced backhand in the seventh game.
The seventh seed upped his level in the second set and the Frenchman gifted him the break in the third game when he whacked a forehand into the net.
Medvedev held onto the momentum from there, leaping into the air to hit a superbly placed backhand shot out of Gaston's reach on break point in the seventh.
Only days after publicly pondering a career in pickleball after his opening-match defeat at Winston-Salem, the mercurial Russian converted another break-point chance in the opening game of the third when he whipped a forehand past the Frenchman.
Czech Jiri Lehecka started his campaign with a 6-1 7-6 4-6 6-2 win over Spain's Pablo Carreno Busta on the Grandstand court.
Shortly before the tournament started, former champion Marin Cilic and 2022 runner-up Casper Ruud pulled out of the US Open due to injuries.
Cilic won the only major title of his career at Flushing Meadows 12 years ago and the Croat was replaced in the draw by lucky loser Otto Virtanen, who faces 23rd seed Andrey Rublev in the opening round.
Virtanen had pulled out of his third round qualifying match against Grigor Dimitrov with injury.
Organisers did not specify what the injury to the 37-year-old Cilic was. The veteran joins a growing list of withdrawals with the likes of Jannik Sinner, Jack Draper, Joao Fonseca and Holger Rune skipping the tournament this year.
