The NHL announced the penalty on its website.
The incident took place at 10:03 of the first period of Boston's series opening 4-1 win Wednesday night, but did not result in a penalty.
With just under seven minutes to go in the first period, Grabovski, 29, was chasing the puck in the Boston zone and ran into Ference's left arm. The latter's elbow made contact with the Leafs centre's head, tossing him to the ice.
"While we agree that Grabovski is eligible for some body contact during this puck chase," Brendan Shanahan, head of the NHL's department of player safety, said in a video explanation, "and that Ference can and should reasonably protect himself against impending hits, the fact remains that Ference cannot initiate a check such as this that recklessly targets Grabovski's head and makes it the principal point of contact."
Shanahan also noted the league did not view the hit as defensive and saw Ference as in control of his own body during the play.
"Although Grabovski is bent over in his pursuit of the puck," Shanahan continued, "he does not change the positioning of his head just prior to or simultaneous with contact in any way that contributes to this illegal check to the head.
"That puts the onus on Ference to avoid this forceful contact entirely, or at the very least hit Grabovski square through the body."
Asked about the hit after the game, Boston coach Claude Julien said he hadn't seen it and couldn't comment.
Toronto coach Randy Carlyle said it was part of the "physicality" of the playoffs.
"It's a game that's made to be physical," he said. "You're allowed to hit people."
It is the first suspension handed out by the NHL this post-season.
There were 12 handed down in the 2012 playoffs accounting for 39 games missed. The bulk of that total came when Raffi Torres — then of Phoenix — ultimately served 21 games for his high, late hit on Marian Hossa of Chicago.
Ference will sit out Game 2 Saturday in Boston (CBC, CBCSports.ca, 7 p.m. ET).