Ovechkin took three shots and delivered several checks. With 3:03 left in the game, Ovechkin got into a shoving match after being run into the boards headfirst by Gregory Campbell. Ovechkin retaliated by slashing Campbell with a one-handed stick swing, and both players earned minor penalties.
The Capitals are unbeaten in three exhibition games.
Jeremy Reich and Brad Marchand had goals for the Bruins.
Perreault and Reich traded first-period goals. With Ovechkin assisting, Perreault connected on a wrist shot from the right circle 8:40 into the game. But Reich beat Michal Neuvirth from the left wing on a counterattack at 14:13.
With 46 seconds left in the second period and Reich serving a minor penalty, Semin gave the Capitals a 2-1 lead. He converted Ovechkin's feed by ripping a hard shot from the left circle past Nolan Schaeffer.
Eakin's goal made it 3-1 with 14:33 remaining in the third. Eakin used defenseman Adam McQuaid as a screen and scored from between the circles.
Marchand scored from the right wing with 9:04 left to get Boston within 3-2.