Sinner converted eight of his 16 break-point chances en route to dispatching Michelsen in 99 minutes on Arthur Ashe Stadium.
In the early goings, Michelsen proved up for the challenge as he twice came back from a break down in the first set, but when Sinner broke a third time for a 5-4 lead he promptly closed out the tightly-contested frame on serve.
Sinner found another gear in the second set and had a much easier time as he raced out to a 3-0 double-break lead to seize control and never looked back as Michelsen's serve suddenly abandoned him.
Michelsen made an encouraging start to the third set but Sinner remained all business and continued applying pressure, eventually earning the decisive break for a 3-2 lead and going on to serve out the match with a routine hold.
The victory was in stark contrast when compared to their first meeting two weeks ago during the second round of a US Open tune-up event in Cincinnati where Sinner prevailed in two close sets en route to lifting the title.
Up next for Sinner, who counts the Australian Open among his ATP Tour-leading five titles this year, will be either Italy's Mattia Bellucci or Australia's Christopher O'Connell.
Ahead of the year's final Grand Slam, the International Tennis Integrity Agency revealed that Sinner had tested positive twice for an anabolic agent in March but avoided a ban as it was ruled he bore no fault or negligence for the violations.
