Diamond, from Guelph, Ont., was immediately ejected after the left-hander's pitch behind Hamilton's head in the third inning of Thursday night's game.
The suspension and undisclosed fine were announced by Joe Garagiola Jr., senior vice-president of standards and on-field operations for MLB.
Since Diamond is appealing the suspension, he remained on the Twins' active roster.
Twins catcher Joe Mauer had been hit by a pitch thrown by Roy Oswalt in the top of the third inning in the series opener Thursday night.
There were no warnings issued after Mauer got hit, but plate umpire Wally Bell quickly tossed Diamond. Manager Ron Gardenhire also got ejected after he charged out of the dugout to protest Bell's decision.
"Anytime in an umpire's judgment they go in the head area, we have to take care of business," Bell said after Thursday night's game. "I felt at the time that he had to be ejected for it."
Diamond insisted he was just trying to pitch inside and "that pitch definitely got away."
Hamilton said before Friday's game that he felt the ball whizzing by the back of his neck. But he didn't think Diamond did that intentionally.
"I don't think he was trying to hit me in the head, I just think the ball got away from him, but it got away from him and it was close," Hamilton said. "It was close, but like I said, I don't think he did that on purpose."
Hamilton said it was the closest a pitch has ever come to hitting him in the head.
"Behind the back of my neck, I could actually feel it when it went by," Hamilton said. "Just feel the wind from the ball when it goes by."Suggest a correction