Grabovski scored the winning goal with 1:01 remaining in regulation as the Toronto Maple Leafs rallied for a 4-3 win that extended Boston's losing streak to three games.
Grabovski and former Bruin Phil Kessel both had two goals each for Toronto, which scored twice in the final 6:33 against the struggling Bruins.
``Grabo was getting hit by everybody on their team and he ended up scoring a great goal - his retribution was to score,'' Toronto coach Ron Wilson said.
It also was a night of retribution for Kessel, booed every time he touched the puck by Boston fans still angered over his holdout that forced a trade to Toronto in 2009. Kessel had never scored against his former team in 10 previous meetings, but ended that skid and another Tuesday.
He batted a high rebound past Tim Thomas to tie the game 1-1 late in the first, then tied it again with 6:33 left with a shot that handcuffed Thomas.
Thomas was frustrated by that goal, then furious after Grabovski's second of the night.
``I was trying to take him and the guy cutting to the back door instead of just taking the shot,'' Thomas said. ``So I left an opening and he took it.''
The Bruins took a 3-2 lead on Patrice Bergeron's 20th goal of the season with 10:52 to play, but failed to hang on and lost for the fourth time in five games.
``Unacceptable,'' coach Claude Julien said. ``I think it's one of those situations where if you have any sense of pride, you're embarrassed about tonight.''
Thomas stopped 24 shots for the Bruins, who have allowed 20 goals in their last four games. Gregory Campbell and Daniel Paille also scored for the Bruins.
Boston continued to struggle in its final home appearance before a six-game road trip. The Bruins were sloppy through the first two periods, then again in the final 10 minutes as Toronto came from behind and left the Bruins stunned.
Kessel jumped on a turnover by Zdeno Chara at the blue-line, got around Andrew Ference for a mini-breakaway and faked out Thomas with a forehand shot to tie the game with 6:33 remaining.
The game appeared headed for overtime until Grabovski, dazed by Chara on a headfirst hit into the boards in the first, took a pass from Clarke MacArthur and beat Thomas.
``I like play like that,'' Grabovski said. ``I like when defencemen play hard against me. It gives me motivation and I play harder and faster.''
Bergeron broke a 2-2 tie with an even-strength goal with 10:52 left. Adam McQuaid fired a shot from the point and Bergeron was in place for the rebound despite getting smothered by defenceman Dion Phaneuf to register his first goal in five games.
Grabovski, who drew a penalty when he was driven into the boards by Chara, put Toronto up 2-1 early in the second on a lucky bounce off Boston defenceman Steven Kampfer's leg for a wide-open backhand.
The Bruins tied it 2-2 with 1:26 to go in the first on a power-play goal. Reimer couldn't handle a shot from the slot by Brad Marchand and Campbell converted the rebound. The play withstood a video review.
Kessel's first goal was also on a high rebound, but his stick was below the crossbar and the goal was deemed OK. The Maple Leafs were already on a power play when Chara was called for boarding, giving Toronto one second of a 5-on-3 advantage. That was enough time for the Leafs to win the faceoff and get a shot from Lupul, who hit Thomas. But the puck bounced right to Kessel for a mid-air conversion.
Paille, coming off a four-game suspension for a blind-side hit on Dallas's Raymond Sawada on Feb. 3, put Boston up 1-0 with 11:56 left in the first when the puck deflected off a Toronto player's skate.
NOTES: The Bruins announced after the game they had acquired centre Chris Kelly from Ottawa for Boston's second-round pick in this year's draft. ... Phaneuf had two assists for Toronto. ... Bergeron has 20 goals in a season for the first time since 2007. ... Toronto picked up Lupul, a centre, in a trade with Anaheim last week. ... Toronto was 2-for-3 on the power play. Boston finished 1-for-4.
1 - 0 BOS
1 - 1 Tie