Trailing 3-2 late in the third period, Reagan Fischer '12 scored a short-handed goal with 54 seconds left in the game to send the contest into overtime. Camille Dumais '13 sealed the victory with the game-winning goal 18 minutes into the overtime period.
"It was a battle," captain Katie Horner '11 said. "It was an emotional roller coaster."
With the series win, Dartmouth (21-10-0, 15-7-0 ECAC) advances to the Eastern Collegiate Athletic Conference tournament semifinals as one of the four remaining playoff teams.
The Big Green will face second-seeded Harvard University in the semifinals on Thursday.
After splitting the first two games in the series and a sluggish first period, both teams' offenses came alive in the second frame.
Jenna Hobeika '12 and Dumais scored in the second period for Dartmouth, while Clarkson junior Brittany Mulligan and freshmen Carly Mercer and Jamie-Lee Rattray recorded goals for the Golden Knights (14-17-6, 10-8-4 ECAC). Clarkson held a slim 3-2 lead entering the second intermission.
The Golden Knights caught a big break late in the third period when Moira Scanlon '12 was called for a five-minute major elbowing penalty. The penalty left the Big Green with a one-skater disadvantage for the remainder of the game.
Head coach Mark Hudak called a timeout, setting a game plan for the remainder of the contest. Dartmouth killed the first two minutes of the power play before pulling goalie Lindsay Holdcroft '14 with approximately a minute left in the game, delivering the team an extra skater in the attacking zone.
The decision paid off for the Big Green. Amanda Trunzo '11 received a rebound and quickly passed the puck to a cutting Fischer, who fired it into the net. The goal sent the crowd of almost 600 fans at Thompson Arena into a frenzy.
"We were really excited," Hudak said. "But for me as the coach, I knew we still had almost two more minutes of penalty to kill off. We still had a game to win."
Neither team was able to score again in regulation, and the contest headed into overtime. The Big Green dominated play in the extra frame, outshooting the Golden Knights, 19-1. Dartmouth could not capitalize on several great scoring opportunities, however, including a shot attempt by Sasha Nanji '13 that went off the post.
"It can be frustrating if you are doing all the little things right but you do not reach your ultimate outcome of scoring a goal," Hudak said. "You just have to continue to do things right."
Dumais finally broke through in the 19th minute, when a shot ricocheted off a diving Clarkson player. Dumais slapped the puck into the net without hesitation.
"It was a beautiful, beautiful goal," Hudak said.
The overtime win marked the first time Dartmouth has won an ECAC tournament game in overtime since a 3-2 victory over Brown University in 2001.
"None of us on the bench really saw the puck go in all we saw was the water bottle flying off," Horner said. "We all just threw ourselves over the bench to chase down Dumais."
The Big Green played on Sunday due to a 4-1 loss on Friday, in which Clarkson overpowered Dartmouth with three goals in the first period. The Big Green bounced back on Saturday with a 4-2 win.
Dartmouth showed significantly more life in the series' second game, twice battling back from deficits to win a close contest.
"We are all at an emotional high and a physical lull right now," Horner said. "We are going to take tomorrow off and I don't think we've ever been as happy to go back to the rink as we will be on Tuesday."
Both ECAC tournament semifinal games will take place on Thursday. Dartmouth will travel to Cambridge, Mass., to face Harvard (17-10-4, 14-5-3 ECAC), while Quinnipiac University will face Cornell University in Ithaca, N.Y.
