WORCESTER, Mass. – Colin Shields was not himself. But the University of Maine’s first-year right winger still managed to do what he does best Sunday: score the game-winning goal as the Black Bears beat archrival Boston University 4-3 in their NCAA Eastern Regional quarterfinal at the Centrum.

Shields, who missed Saturday’s 4-3 overtime win over Harvard due to an allergic reaction to medication for an infected (and extracted) tooth that left him bed-ridden, scored his 29th goal of the season with 4:23 left Sunday to send the Bears to the national semifinals.

The 25-10-7 Black Bears will make their third trip to the Frozen Four in four years and will take on 30-6-3 New Hampshire in a 1:30 p.m. semifinal on Thursday, April 4, at the Xcel Energy Center in St. Paul, Minn. Minnesota and Michigan play in the 7:30 p.m. semi.

New Hampshire nipped Cornell 4-3 later Sunday. BU finished at 25-10-3, including a 0-3-1 mark against Maine in the last three weeks.

“Just because Colin had an infected tooth didn’t mean he was going to have a bad shot,” said Maine junior right wing Lucas Lawson, who had sandwiched a pair of third-period goals around one by BU freshman center David Klema to give the Bears a 3-2 lead.

After Shields had given Maine some breathing room, Klema scored 1:21 later to set up a wild finish. BU had four offensive zone faceoffs with goalie Sean Fields pulled in favor of the extra attacker, but they failed to convert.

Shields’ game-winner, his team-leading sixth of the season and his ninth game-winning point, came about when a loose puck drifted into the BU zone. BU senior defenseman Chris Dyment lumbered back after it but Shields beat him to it.

“He was going back slowly. I don’t know if he had been out there awhile or what. I got past him, got good body position and got off a quick shot,” said Shields. “I was thinking five-hole the whole way. I made a little fake before I reached the puck and I think it froze the goalie.”

Shields said he was significantly weaker than usual but felt well enough to play.

“I was pretty weak. I felt better this morning but had a bad headache and I hadn’t eaten anything, just a little snack. I wasn’t strong along the boards and after taking a couple of hits in the first period, I felt they took a lot out of me. So I tried to avoid contact,” said Shields. “In the third period, they hemmed us in for a couple of shifts and I got some energy and some of my breath back. I used that little bit of extra fuel in my tank to win the race to the puck.”

Maine never trailed in the game.

Robert Liscak staked the Bears to a 1-0 lead 3:47 into the game but Mike Pandolfo equalized on the power play 3:27 later.

After piling up 18 second-period shots without a goal due to the sharp goaltending of Fields, Lawson’s tally made it 2-1 on the power play 3:48 into the third period. Klema answered a 10:14 but Lawson scored 40 seconds later to give Maine a lead it would not relinquish.

Paul Falco had come to the bench on a line change and Lawson jumped off the bench to replace him.

Prestin Ryan took a wrist shot and Maine freshmen Ben Murphy and John Ronan drove to the net to create a wild scramble. With bodies strewn across the crease, Lawson found the puck on his stick to the left of Fields.

“I was on the backhand and I just put it on net. I think it may have hit one of their players and went in,” said Lawson, whose goal was his 17th of the season. “If you throw the puck on net, good things happen.”

Klema got that one back when he received the puck from Mark Mullen and jammed the puck off Maine goalie Matt Yeats’ pads from behind the net.

Liscak had opened the scoring when he found himself all alone in front of Fields and slid a 10-footer inside the far post off a Peter Metcalf pass from the left wing boards.

Pandolfo tied it when he gathered in a Brian Collins rebound in the slot and wristed a 20-footer inside the left post.

BU freshman right winger Justin Maiser was assessed a five-minute major and a game disqualification for spearing Francis Nault at the 10:41 mark but the Bears were unable to generate many quality chances as the Terriers did an exceptional job killing off the penalty.

But BU coach Jack Parker said Maiser’s absence the rest of the game hurt his team.

“We wanted to match lines and we had a specific way we wanted to play. We couldn’t do that,” said Parker. “Killing off that penalty also left us a little legless. It was a dumb penalty to take.”

Although the Bears were frustrated by Fields in the second period, they entered the third period with confidence.

“The BU players looked tired at the end of the period and we were flying,” said Maine junior center Liscak.

Maine senior defenseman and captain Peter Metcalf observed “BU was playing only five ‘D’ (defensemen) and they were using only two or three lines and we were rolling four out there.”

Lawson’s power-play goal broke the 1-1 tie as he took a Liscak pass at the side of the net and scored from a difficult angle.

“Fields went down and I put it upstairs, short side,” said Lawson.

It was Maine’s ninth straight game with at least one power-play goal.

Klema tied it when he took a Ken Magowan pass, pushed it ahead of a Maine defenseman along the right wing and beat Yeats.

“I think the shot went through him,” said Klema.

Yeats finished with 31 saves, including 10 Grade-A stops, to run his career record to 5-1-3 against BU.

“They’re my favorite team to play against. They always throw the puck to the net so I always have to be ready,” said Yeats.

“He has played great against us throughout his career,” said Parker. “I know he’s had his struggles this year but he must love seeing the Red and White BU jerseys.”

He also credited Yeats’ teammates for their performances.

“Maine did a great job in every area. They did a great job forechecking and backing off, forechecking and backing off, and they didn’t give us many second shots, ” said Parker. “It was a well-fought, well-refereed game. The better team won.”

Fields made 30 stops, including 14 Grade-As.

Maine interim head coach Tim Whitehead was ecstatic with the win, saying, “I’m proud of our players. They weren’t going to be denied. We built some momentum and tempo at the end of the second period and early in the third and it was a statement to BU that we were going to stay with them.”

BU had the bye as the second seed while Maine had to go overtime Saturday to beat Harvard.

Whitehead’s win was the 101st of his coaching career including his five years at UMass-Lowell.

Metcalf, who was seen making the sign of the cross in the waning seconds of the game, admitted that the end was “nerve-wracking.

“They had the momentum but Maine hockey was not going to be denied,” said Metcalf.

BU left winger and captain Pandolfo said, “We weren’t as good as we had to be. They took it to us, they won most of the one-on-one battles for the puck, and we couldn’t find a way to win.”

Lawson, Metcalf and Yeats of Maine headlined the East Regional All-Tournament Team. Colin Hemingway of New Hampshire, BU’s Klema and Doug Murray of Cornell also were selected.

BLACK BEARS 4, TERRIERS 3

Maine (25-10-7) 1 0 3 ? 4

Boston Univ. (25-10-3) 1 0 2 ? 3

First period ? 1. Maine, Liscak 14 (Metcalf) 3:47; 2. BU, Pandolfo 22 (Collins) 7:14; Penalties: Maine, Nault, interference, 2:06; BU, Maiser, tripping, 3:10; Maine, Reimann, holding the stick, 6:11; BU, Maiser, spearing (five-minute major, game disqualification), 10:41; Maine, Ryan, roughing, 15:58; BU, Johnson, roughing, 15:58; Maine, Shields, hooking, 16:36

Second period ? No scoring; Penalties: Maine, Nault, hooking, 10:07; BU, Meyer, high sticking, 10:55; BU, Magowan, holding, 15:43

Third period ? 3. Maine, Lawson 16 (Liscak, Nault) 3:48; 4. BU, Klema 5 (Magowan, Bussoli) 10:14; 5. Maine, Lawson 17 (una.) 10:54; 6. Maine, Shields 29 (una.) 15:37; 7. BU, Klema 6 (Mullen, Cronin) 16:58; Penalties: BU, Greeley, holding, 2:15; Maine, Metcalf, slashing, 7:41

Shots on goal: Maine 11-18-5?34; BU 10-11-13?34

Goaltenders: Maine, Yeats (34 shots-31 saves); BU, Fields (34-30)

Power-play opportunities: Maine 1 of 5; BU 1 of 5

High-percentage scoring chances: Maine 12-9-5?26; BU 5-5-11?21

Attendance: 11,888