Scoring only his second goal of the season, Boston defenseman Mike O'Connell hit a tie-breaking 50-foot slap shot at 14:36 of the third period to give the Bruins victory over the Chicago Black Hawks, 4-2, in Boston yesterday.

"We kept plugging away," said Boston Coach Gerry Cheevers. "It was a nice victory over a top team."

Chicago took a 2-0 lead on Al Secord's 24th and 25th goals of the season before the Bruins fought back to extend their unbeaten home streak to nine.

Barry Pederson, who pulled the Bruins to 2-2 with his 19th goal of the season, at 5:08 of the third period, ensured the victory by scoring into an empty net with 35 seconds remaining.

"You can't take a two-goal lead and play the rest of the game in your end and get away with something," said Chicago Coach Orval Tessier. "Boston is an excellent hockey team, but I'm certainly disappointed in our performance. We tried to back in and play behind our net for 40 minutes, and it didn't work very well . . . We have an awful lot of good hockey players who were tourists here today."