It all came down to power plays and a well-timed trap.

Boston College goalie Matti Kaltiainen stopped 17 first-period shots, then the Eagles ground the Boston University offense to a halt with a 1-2-2 trap in the second period, scoring two power-play goals late in the period after forcing the Terriers into numerous icings and neutral-zone turnovers.

Altogether, the Eagles went three-for-five with the man advantage while skunking the Terriers on six power-play chances.

In the end, No. 8 BC (13-5-3, 9-3-1) came away with a 3-1 road win over No. 12 BU (13-8-2, 7-6-0), as Dave Spina scored two goals and an assist while Kaltiainen stopped 26 of 27 shots for the Eagles. Ben Eaves scored the other Eagle goal, while Terrier captain Freddy Meyer had the lone tally for BU in front of 3,744 at Walter Brown Arena.

Although any win between these archrivals is savored, this one had to be particularly satisfying for the Eagles, who played without top defenseman J.D. Forrest (quad injury) as well as minus freshman phenom Patrick Eaves, who is sidelined indefinitely with a neck injury.

“We work hard on power plays,” Spina said. “Tonight it was definitely clicking. It’s been an up-and-down year because of injuries and changes in lines, but I think this shows tonight that we can put different guys in different roles and still be successful.”

“Matti was very strong in the goal, especially when they had the four-on-three [in the first period],” Eagle coach Jerry York said. “Probably special teams and Matti’s strong performance were the difference in the game — an exciting game to watch.”

For the second time this season, Terrier coach Jack Parker saw his troops lose a defensive-minded struggle at home against BC. “The real story of the game was that we were really after them in the first period and dominating the period even though we were down one-nothing.

“Then in the second period, they started trapping with a 1-2-2 trap down low and in center ice and slowed the game down to a crawl,” Parker said. “And we just couldn’t generate anything through center ice … slowed the game and got two power play goals to boot. Real good move by Jerry and real good execution by the team to play that and to slow the game down like they did.”

BC came out more physical than usual and dominated territorially on its first power play of the game, culminating in a goal. Playing the point in Forrest’s absence, Ryan Shannon’s slapshot went wide of the net but bounced off the lively Walter Brown boards and out to Ben Eaves on the opposite side of the net. Shooting up high just as the puck came back over the goal line, he had a bad angle but buried it cleanly at 7:31.

BU got the physical game going as the period wore and had any number of good chances, most notably with the four-on-three advantage in the period’s last five minutes. Kaltiainen made good saves, and the Terriers helped out by putting the puck over the net or wide several times.

“We kind of made a decision,” York said of the Finnish netminder. “We were watching, alternating Timmy [Kelleher] and Matti. We thought after the New Year we’d pick the hotter of the two goaltenders and just ride with that goaltender. I think it gives a little more rhythm to your team.”

The Eagles dramatically turned the tide in the second period with the aforementioned trap, outshooting the Terriers 13-4. BU goalie Sean Fields kept it 1-0 for quite some time, thwarting Tony Voce and Ty Hennes on a two-on-one at 10:51, then making an excellent save on a short-range slapper by Andrew Alberts during a brief four-on-three for the Eagles at 17:20.

Alberts got his revenge seconds later, assisting on the Eagles’ second goal. Fields stopped his initial shot from the point, but from the side of the net Voce cleverly slid the puck behind Fields, inches in front of the goal line. It was an easy tap-in for Spina on the far side of the net.

After Brad Zancanaro was called for playing without a helmet at 18:32, Spina got his second goal and a beauty off of a nice feed from Eaves. In a scrum along the boards that drew the Terriers out of the slot, Eaves slipped the puck to Spina all alone at the right-wing faceoff dot. He went in and flipped a high backhander into the net on Fields’ stick side.

“Just a great hustle play by Eaves and Voce,” Spina said. “The thing about Benny is he just has this extra something that a lot of players don’t have. He just opens the ice up and gives you that extra second to score or make a play. Every time you’re on the ice with him, it’s a special moment.”

Oddly enough, Spina now has three two-goal games this season despite only scoring nine goals total in 19 games.

The Terriers fared much better in the third period in terms of getting into the BC zone for chances. At 3:10, Brian Collins nudged the puck on a faceoff in the Eagle end, and then the puck sat there for several seconds while a few pairs of players from the two teams tangled each other up. Finally Meyer picked up the puck, wheeled, and beat Kaltiainen low to make it 3-1.

Unfortunately for the Terriers, they couldn’t get their power play on track, generating just seven shots on their six opportunities. Five on five, they almost got a second goal at 14:00 when Brian Collins’ pass from behind the net hit Dan Spang crashing the net, but the shot went just wide. At 15:40, off of a Kenny Magowan rush and pass, Zancanaro came close and something approximating a spin-o-rama move.

Parker pulled Fields early — right after a timeout with 2:41 to play — and several nominal chances ensued as well as a few Eagle near-misses on the empty net. Yet neither team could score, and that’s how it ended.

The teams play a rematch Friday night at the Conte Forum.