ORONO – Freshman defenseman Matt Duffy had been a healthy scratch for nine consecutive games. But when junior Mike Lundin suffered a badly sliced pinky finger and a fractured bone four games ago, Duffy received his opportunity to return to the University of Maine men’s hockey lineup.

The Windham native capped off an impressive four-game stretch with his first two collegiate goals Saturday night, including the game-winner, as the Black Bears survived a stern challenge from UMass Lowell to nip the tenacious River Hawks 4-3 and sweep their Hockey East quarterfinal series.

The 26-10-2 Black Bears, the second seed, advanced to the Hockey East semifinals for a league-leading 17th time and they will face No. 3 Boston College (22-11-3) in Friday’s 8 p.m. matchup at the TD Banknorth Garden.

Top seed Boston University (23-9-4) will meet New Hampshire (20-11-7) in the 5 p.m. opener.

The championship game will be Saturday at 7.

Duffy’s first-period goal answered one by UML’s Bobby Robins just 28 seconds into the game and his second finished off a span of three goals in 5:27 early in the second period to build the lead to 4-1. Greg Moore and John Hopson scored the first two goals of the flurry.

J.R. Bria and Andrew Martin scored power play goals just 22 seconds apart later in the second period with Bria’s coming with a two-man advantage but Maine freshman goalie Ben Bishop made eight third-period saves to preserve the win.

“Since I wasn’t playing, I was always on the ice, getting as much practice as I could in order to get better,” said Duffy. “I finally got my chance to get back in and prove I could play. I can’t believe I scored two goals in one game. If I had gotten a hat trick, I would have passed out.”

Senior captain and right wing Greg Moore said, “This was an unbelievable time for Matt to step up. A lot of guys have been contributing, guys who haven’t even been in the lineup [regularly]. That’s what you need at the end of the season and during the playoffs. That has definitely helped our success lately.”

Maine extended its unbeaten streak to 10 games (8-0-2). Maine is 12-0 against UML in the Hockey East playoffs.

Maine’s 11th consecutive win over the River Hawks also involved some good fortune as the River Hawks hit the post three times in the first period and had a goal disallowed because the whistle had blown before the puck entered the net.

UML goalie Peter Vetri said, “Things didn’t go our way tonight. We hit all those posts. It could have been a wide open game after the first but it wasn’t. Maine made the plays and deserved what they got.”

River Hawk captain Robins said, “We poured out everything we had. We gave it our best shot.”

Moore said “They played unbelievable. I knew it would be a tough weekend but they proved to be even tougher than expected.”

Robins quieted the crowd by skating unattended from the left wing boards and across the crease before depositing the puck in the open net.

But Duffy equalized with a screened snap shot from the left point that evaded Vetri.

“I didn’t see it until it hit my stick and went in,” said Vetri.

Moore made it 2-1 just 27 seconds into the second period when he took a cross-ice pass in full stride from Michel Leveille and fired a slap shot from the top of the right circle that deflected in off Vetri’s shoulder.

Leveille’s assist was his 100th career point.

Hopson scored on the power play as Simon Danis-Pepin’s low slapper from the top of the right circle deflected in off his skate.

Duffy made it 4-1 53 seconds later off a Leveille feed on a two-on-one.

“I knew he [Vetri] wasn’t going to be quick enough to get over because it looked like [Leveille] was getting ready to shoot. [Leveille] made a great pass and I just one-timed it to the net and it went five-hole,” said Duffy.

Vetri said “It was a good pass and a good finish. He caught me in transition. I opened my legs up and it went through.”

But the momentum changed dramatically when Bria’s shot from the right point snaked inside the far post and Martin banged home an Elias Godoy rebound.

Despite going 10 minutes without a shot on goal in the third period, Maine limited UML to just four high-percentage opportunities.

Bishop made a game-saving glove stop on Bria’s blazing one-timer from the right point and he made a few critical stops during a wild flurry at the edge of his crease, including a wraparound attempt, in the waning moments.

“It was close but he stood up to us,” said UML senior center Brad King.

Bishop said, “Our guys played a great third period. They did a great job in front of me.”

A dejected Vetri said, “You need big goaltending in the playoffs to be successful and their goalie outplayed me.”

Bishop finished with 22 saves while Vetri had 24.

BLACK BEARS 4, RIVER HAWKS 3

UMass Lowell (14-20-2) 1 2 0 – 3

Maine (26-10-2) 1 3 0 – 4

First period – 1. UML, Robins 13 (King), :28; 2. Maine, Duffy 1 (Wight, Moore), 11:20. Penalties: Maine, Ramsey, interference, 3:29; Maine, Jankus, hooking, 6:00; UML, Brandvold, 11:44; Maine, Bellamy, roughing, 11:44; UML, Kinley, hooking, 13:20; Maine, Shepheard, hooking, 16:17; Maine, Damon, hooking, 17:38.

Second period – 3. Maine, Moore 26 (Leveille, Wight), :27; 4. Maine, J. Hopson 7 (Danis-Pepin, Ryan), 5:01 (pp); 5. Maine, Duffy 2 (Leveille, Moore), 5:54; 6. UML, Bria 5 (Godoy, Tejchma), 12:14 (pp); 7. UML, Martin 7 (Godoy, Pandolfo), 12:36 (pp). Penalties: UML, Pandolfo, holding, 4:03; Maine, Johnson, obstruction-interference, 10:17; Maine, Bishop (served by Bellamy), tripping, 10:58; UML, Collar, holding, 16:44.

Third period – No scoring. Penalties: UML, Brandvold, hooking, :52; Maine, Jankus, hitting from behind, 3:39; Maine, Jankus, roughing, 6:02; UML, Vetri (served by Potacco), diving, 6:02; Maine, Tyler, cross checking, 6:23; UML, Brandvold, hooking, 10:01; Maine, Bellamy, holding the stick, 10:01.

Shots on goal: UML 8-9-8-25; Maine 11-12-5-28

Goaltenders: UML, Vetri (28 shots-24 saves); Maine, Bishop (25-21)

Power-play opportunities: UML 2 of 8; Maine 1 of 4

High-percentage scoring chances: UML 5-6-4-15; Maine 7-8-4-19

Attendance: 4,508