Making his NHL playoff debut after being called up Wednesday from Providence of the American Hockey League, Fraser jumped into a scramble in front of goalie Carey Price and slid the puck under him into the net.
Tuukka Rask made 33 saves for Boston, and Price stopped 34 shots.
Game 5 is Saturday night in Boston.
DUCKS 3, KINGS 2
LOS ANGELES (AP) — Teemu Selanne scored the tiebreaking power-play goal late in the second period, Corey Perry got his first goal of the series, and Anaheim trimmed Los Angeles' series lead to 2-1 in the Western Conference semifinals.
Jonas Hiller made seven saves in the final 9:58 after rookie goalie Frederik Andersen left with a right leg injury for the Ducks, who bounced back from two narrow losses in Anaheim to open the series.
Ben Lovejoy added a goal with 2:55 to play as Anaheim snapped the Kings' six-game winning streak.
Game 4 is Saturday night at Staples Center.