Apart from the opening game of the match, when he recovered from 0-40 down to hold serve, Sinner was rarely troubled by world number 93 Gaston.
Playing his first official match since winning the ATP Tour Finals in November, Sinner sent down three aces and an unreturnable serve during a run of five consecutive points to avoid that early break.
He lost only nine more points behind his serve in the remainder of the match, served six aces in all and did not commit a double fault, ending with a first-serve percentage of 64%.
Four-time Grand Slam champion Sinner reeled off four consecutive breaks of serve as he won nine games in a row, moving from 2-2 in the first set to the brink of a two-set lead.
Gaston avoided a second-set bagel by holding serve at 5-0 down but the left-hander, who briefly received treatment at the end of the first set, elected to end the match after losing the second.
“Obviously it’s not the way you want to win the match. I wish him a speedy recovery and hope it’s nothing too bad,” added Sinner, who will face Australian wildcard James Duckworth in round two.
