United led by a solitary point at halftime but piled on 29 points in a dominant third term.
Much of that was down to Blanchfield, who worked hard to find space and seemingly couldn't miss from deep.
Melbourne's defensive efforts were much improved in the second half too, personified by Cedric Jackson sprinting the floor to block a Harris layup in one of the plays of the game halfway through the final term.
Tai Wesley chipped in 10 points off the bench, while 206cm power forward Majok Majok (nine points, 11 rebounds) impressed with his work on the low post.
Melbourne host the Brisbane Bullets on Thursday, while the 1-2 Hawks will travel to Perth to face the reigning champion Wildcats on Friday.
Hawks coach Rob Beveridge said his side shot poorly from beyond the arc and gave up too many open looks to Melbourne, who did a far better job of capitalising.
"It's pretty disappointing that they were able to do that," he said.
"That was the difference, purely. They shoot 70 per cent, we shoot 24 - there's the game right there. We lose by 12 and it could have been a lot worse."
Melbourne coach Dean Demopoulos said it was a much-improved performance from the highly-fancied United but cautioned that the team remained a work in progress.
"We weren't quite as bad as people thought the first couple of games and we're not quite as good as some people might think now," he said.
"We're not drowning anymore, we're sea level - for now, anyway - and we just want to build on it."
- AAP
