Merrimack suffered its most significant loss of the season the same night it posted its most impressive win.

Moments after notching the first hat trick of his college career in Saturday night’s 6-1 manhandling of No. 4 Boston College, Warriors junior Marco Rosa was reported lost for the season with what was diagnosed as a fractured right wrist.

Rosa was taken to [nl]Lawrence (Mass.) General Hospital for X-rays shortly after the game following a vicious collision behind the BC net with Eagles defenseman Andrew Alberts midway through the third period. Alberts received a minor penalty for elbowing on the questionable hit while Rosa received a standing ovation on his way to the trainer’s room from the appreciative 2,753 inside the Volpe Center.

Rosa, who nearly won Friday night’s 3-2 overtime loss to the Eagles in the waning seconds of regulation, scored a goal in each period, including two on the power play, before the injury occurred.

“I was sky high walking through the [locker room] door, then the first guy I see is our orthopedic surgeon,” said dejected Merrimack head coach Chris Serino. “He tells me [Rosa] has a broken wrist and is done for the year. So that put a little damper on things right away.”

Rosa, whose parents, brother and sister-in-law had made the trip Saturday from Mississauga, Ontario, had broken a four-way tie for the team lead in goals just 28 seconds into the third period with his third of the night and 10th of the season. He swept a Matt Johnson (3 assists) rebound past BC goalie Tim Kelleher while being knocked to the ice, giving the Warriors a commanding 4-0 lead.

“I told the guys that Marco may not play every game great, but he plays every game hard and every shift hard,” Serino said. “Maybe we don’t have him anymore, but we owe it to him to play like he does the rest of the way.”

Rosa’s injury overshadowed an exceptional team effort from the Warriors in shutting down the highly skilled Eagles and another spectacular goaltending performance from senior captain Joe Exter (27 saves), who was called upon early to keep his club in the game.

“I thought Exter was very good in the first period,” said BC head coach Jerry York, whose club remains a point ahead of both New Hampshire and Maine for first place in Hockey East despite the loss. “We created a lot of good chances, had some real good jump. And then finish the period down 2-0.

“They didn’t have many opportunities in the first period, but they capitalized on two misplays by us,” York said. “Then Merrimack took over in the second and third period.”

From the onset, the Warriors showed no signs of feeling sorry for themselves following Friday night’s crushing overtime loss at the Heights.

Just seconds after Exter robbed BC junior Tony Voce, who was back in the lineup following a one-game team suspension, on a 2-on-1 break, Brent Gough jammed in a Johnson centering pass that slipped under BC defenseman Brett Peterson’s stick just 3:51 into the first period. The goal ended a seven-game scoreless streak for the freshman.

Almost 13 minutes later, Rosa forechecked the puck around Kelleher then wristed on net a wobbly shot that the BC netminder had trouble controlling. While trying to stab the puck with his glove, Kelleher, who hadn’t started since Dec. 27, lost his balance, falling to out of the crease as the puck trickled over the goal line.

The play was so slow in developing that referee Tim Benedetto and Gough both signaled for the goal at 16:56 before the goal judge could turn on the red light.

Rosa scored his second goal on the power play with a turn-around blast from 35 feet out that deflected off BC forward Ryan Murphy’s stick over Kelleher’s right shoulder at the 12:59 mark of the second period for a 3-0 lead.

Trailing 4-0, the Eagles’ lone goal came from freshman Stephen Gionta, who lifted a Peterson rebound high into a partially open net over a diving Exter with 15:47 left in the game.

Merrimack sophomore Steve Crusco scored 1:29 later, sent in alone on Kelleher with a perfect 50-foot pass through the BC defense by defenseman Cam DeYoung, to give the hosts back their four-goal cushion.

After the Rosa injury and with most of the Warriors trying to pay back Alberts, freshman defenseman Rob LaLonde scored Merrimack’s third consecutive power-play goal on a give-and-go play with Crusco, rocketing a slapshot over Kelleher (18 saves) from 30 feet out. Failing to score on its first man advantage last night, the Warriors were in a 0-for-17 slump on the power play spanning more than five games.

The loss was the first for Kelleher against Merrimack in six starts over three seasons. The junior had previously twice shut out the Warriors while posting a 1.40 goals-against average in his five straight wins.