The Italian was playing for the first time since defeating Carlos Alcaraz in the Wimbledon final and showed no difficulty in adjusting to the hard court, dispatching his opponent in just 59 minutes
Although Galan showed glimpses of promise with his serves and forehands, the match always looked like Sinner's to lose.
The first set was completed in just 26 minutes, with the Italian twice breaking Galan who failed to convert his only opportunity to do the same. Early in the second set, the Colombian produced his best tennis of the match, but even that caused little trouble for the World No.1.
Sinner dropped just two games throughout the whole match against the World No. 144, setting up a Round of 32 match against either Sebastian Baez or David Goffin.
The 23-year-old is looking to retain his title having won at this venue 12 months ago. It was that win that kickstarted a remarkable run for the Italian with his record at 48-2 in big tournaments since then.
One obstacle to the Italian's success could have been the balls, which Sinner claimed had got smaller.
"From my point of view, the tennis balls are getting smaller," he said ahead of his Round of 16 match. "The more you play, the smaller they get.
"That is very strange because usually they open up and get slower, but here they get actually faster.
"The ball bounces much higher. We haven't had one very windy day yet, but it's going to be very difficult if there's going to be wind here.
"We saw it last year, remember the match against Andrey was super difficult, so it's very difficult and it's going to be a mental game. I am trying to accept every situation on the court and trying to be ready."
Sinner was also seen wearing a strap around his arm, as he did at Wimbledon, and revealed it was more to do with comfort then protecting an injury.
"The elbow does not hurt, but I like the sensation that gives the sleeve," he said.
"It gives a little more stability in the impact with the ball. I had also used it at Wimbledon and I liked it."