BOSTON -- This year, the Washington Capitals appear to have saved their best for the postseason.

Joel Ward slammed home a rebound at 2:57 of overtime to give Washington a 2-1 victory over Boston in Game 7 of their first-round playoff series on Wednesday night, sending the Capitals to the Eastern Conference semifinals and ending the defending Stanley Cup champion Bruins' hopes of a repeat.

Rookie Braden Holtby stopped 31 shots for Washington in the seventh one-goal game of the series. Matt Hendricks also scored for the Capitals, who barely made the playoffs this year after finishing atop the Eastern Conference in each of the previous two seasons -- and winning just one postseason series combined.

"It's a nice sense of accomplishment to be able to get over the hump," Capitals defenseman Karl Alzner said. "It's nice to turn the page, and maybe we're writing a new script."

Tim Thomas made 26 saves for Boston, which was hoping to become the first team to repeat as Stanley Cup champions since the Detroit Red Wings in 1997-98. Tyler Seguin scored the Bruins' only goal.

It was the first time in NHL history that a playoff series had seven games determined by one goal. Four of the games went to overtime, and two others were decided with less than two minutes left in regulation.

"It was very close," Boston defenseman Zdeno Chara said. "We shouldn't be disappointed in what we did this season. We just came up short."

Hendricks scored midway through the first period, and Seguin tied it in the second. It stayed that way through a scoreless third, with Washington killing off a penalty in the final 3 minutes to send the game into overtime.

Patrice Bergeron had a chance to win it in the first minute of the extra period, but he couldn't get off a solid shot from Holtby's right. Two minutes later, the Capitals broke into the Boston zone with former Bruin Mike Knuble leading a 2 on 1.

Knuble shot, and Thomas left the rebound out where Ward could reach it with his backhander.

"When I saw the puck there, I just took a whack at it," Ward said. "It was a sense of relief, a great accomplishment."

The building fell silent as the Capitals celebrated just their third postseason series win since a run to the Stanley Cup finals in 1998. Some fans littered the ice with debris, but the Bruins waited patiently for the postgame handshake.

Thomas, the reigning Vezina and Conn Smythe Trophy winner, gave Holtby a tap on the shoulder and said, "Great job, kid."

"I'm proud of our team against the defending Stanley Cup champs," said Holtby, a third-stringer making his playoff debut because of injuries to Tomas Vokoun and Michal Neuvirth. "I don't get rattled. It's one of the things I learned: To be able to get to this level you have to be like that."

The Capitals earned more than 100 points in the previous three seasons, leading the NHL with 121 in 2010, but had little to show for it once the postseason started. They won just two series in three years and have not made it out of the East semis since 1998, when they made it to the Stanley Cup finals but were swept by Detroit.

This year's regular season wasn't as successful, with coach Bruce Boudreau fired in November and replaced by Dale Hunter.

But the playoffs have a chance to be even better.

Waiting until the final games of the season to clinch a playoff berth and getting bumped up to a No. 7 seed on the final day, the Capitals won three times in Boston -- they also won Games 2 and 5. Their second-round opponent won't be determined until after Game 7s Thursday night between Ottawa and the New York Rangers, and Florida and New Jersey.

"I'm not going to watch the games," Capitals forward Alex Ovechkin said. "I'm just going to chill and control my moods and control emotions."

The Bruins needed an unprecedented three Game 7s to win the Cup last year, including the 4-0 victory over Vancouver that gave the Original Six franchise its first title since 1972. Thomas also had a shutout in the Game 7 win over Tampa Bay in the Eastern Conference finals.

But that streak ended midway through the first period when Carlson shot from right point and Hendricks tipped it past Thomas' right shoulder to give the Capitals a 1-0 lead.

The Bruins tied it with 5:33 left in the second when Holtby kicked Andrew Ference's shot wide to his left to Johnny Boychuk, whose shot trickled through the goalie's pads and into the crease. Seguin dove for it, with two defenders crashing on top of him, and swiped it into the net to make it 1-1.