The Leafs last scored 10 goals in a game in 1998. Toronto, trailing 2-1 after one period, scored five times in the second. After Bates Battaglia and Steen scored to help Toronto regain the lead, 3-2, they each struck again along with Kris Newbury in a span of 42 seconds to make it 6-2 with 3:45 remaining in the period.
Steen began the night with only 10 points.
Also scoring for the Leafs were Matt Stajan, with two third-period goals, Chad Kilger and John Pohl. Ian White, Boyd Devereaux and Tomas Kaberle each had two assists.
The Leafs moved three points ahead of last-place Boston in the Northeast Division. It was only their second road victory since Nov. 24.
It was the seventh meeting of the teams. Toronto has outscored Boston 21-7 in its three victories while being outscored 12-4 by Boston in its four losses.
The Bruins lost their third straight, including 5-1 Tuesday in Toronto, and have been outscored 20-3 in the last three games.
After Pohl gave Toronto a 1-0 lead in the fourth minute, Shean Donovan and Wayne Primeau responded with a pair of goals over the next 7:23 to put the Bruins ahead 2-1.
Battaglia tied it 2-2 when he knocked in the rebound of a White shot, beating goalie Tim Thomas at 1:36 of the second.
Steen put the Leafs ahead 3-2 at 8:24 on a great individual effort when he drove toward the net and beat Thomas while falling into the crease.
Thomas allowed eight goals in losing for only the second time in eight appearances against the Leafs. Philippe Sauve took over late in the second period and allowed two goals on eight Toronto shots the rest of the way.
Andrew Raycroft made 29 saves to earn the goaltending win.
Toronto had a 39-31 shots advantage. On power plays, Toronto was 1-for-5 and Boston was 1-for-7.
Notes: Darcy Tucker was out of the lineup for Toronto after returning last game. He was one of five Leafs forwards that missed the game . . . The Leafs scored five goals in a period for the second time this season . . . Toronto's record for fastest three goals is 39 seconds occurring on Jan 20, 1940 . . . The Leafs returned home to face the Buffalo Sabres on Saturday.