Washington (36-15-5) will finish second in the MassMutual East Division and have home-ice advantage against third-place Boston (33-16-7) in the best-of-7 series.
Game 1 will be at Washington on Saturday (7:15 p.m. ET; NBC, CBC, SN, TVAS).
The Bruins went 4-2-2 against the Capitals this season, outscoring them 26-24.
"A solid team. Great top six (forwards), big bodies," Bruins coach Bruce Cassidy said after a 3-2 overtime win against the New York Islanders on Monday. "The coach (Peter Laviolette) has been there many times, so they're going to be ready to go. Obviously playing [Zdeno Chara], I'm sure that will become a storyline. But again, a team we've played well against this year. Looking forward to the matchup."
Chara, a defenseman, was Boston's captain for 14 seasons before agreeing to a one-year contract with Washington on Dec. 30.
"He knows when we're doing certain plays," Bruins forward Brad Marchand said. "Obviously, teams will do video and stuff like that, but he knows all the code names that we use and typically the situations that we like to use them in. So even when we played them this season, we could see him talking to guys about the plays that we were going to do. So it could definitely cause some challenges at times. But it's playoffs, you've got to work through that there."
Capitals center Nicklas Backstrom said he thinks it's a big advantage to have Chara for this series.
"Obviously it can mean a lot. He's been there for many years," Backstrom said Tuesday. "They haven't really switched that much. He can be an asset for us, knowing what they're doing on face-offs and stuff like that. That's huge in the playoffs. Small things like that is going to change the series I think. Yeah, hopefully we can take advantage of that."
The Capitals, who went 4-4-0 against the Bruins, were led by Backstrom with nine points (one goal, eight assists) and forward T.J. Oshie with eight (five goals, three assists) against them. Forwards Lars Eller (three goals, one assist), Alex Ovechkin (two goals, two assists) and Jakub Vrana (one goal, three assists), and defenseman John Carlson (one goal, three assists) each scored four points. Rookie Vitek Vanecek was 4-3-0 with a 2.86 goals-against average and .905 save percentage in seven games against Boston. Ilya Samsonov was 0-1-0 with a 3.66 GAA and .872 save percentage in two games (one start).
Marchand led the Bruins with 13 points (seven goals, six assists) against the Capitals, followed by forwards Patrice Bergeron with nine (three goals, six assists), David Pastrnak with eight (three goals, five assists) and Craig Smith with seven (three goals, four assists). Jaroslav Halak was 2-0-0 with a 2.01 GAA and .931 save percentage in two games, Tuukka Rask was 1-0-2 with a 2.59 GAA and .905 save percentage in three games, and rookie Jeremy Swayman was 1-1-0 with a 2.00 GAA and .938 save percentage in two games. Rookie Dan Vladar made 25 saves in an 8-1 loss April 11.
Backstrom led the Capitals with 53 points (15 goals, 38 assists), followed by Carlson with 44 (10 goals, 34 assists). Oshie scored 43 points (22 goals, 21 assists), and Ovechkin scored 42 points, including a Washington-high 24 goals, in 45 games.
Vanecek went 21-10-4 with a 2.69 GAA, a .908 save percentage and two shutouts in 37 games (36 starts). Samsonov was 13-4-1 with a 2.69 GAA, a .902 save percentage and two shutouts in 19 games (18 starts). Craig Anderson was 2-1-0 with a 2.13 GAA and .915 save percentage in four games (two starts).
Ovechkin returned for a 2-1 win against the Bruins on Tuesday after not playing in seven of the previous eight games because of a lower-body injury.
"Not every game has turned into a win, but we were able to keep our head above water and we're able to win hockey games regardless of the lineup," Laviolette said. "To me, that shows a perseverance inside the room. That guys are able to jump into roles and jump into positions and help our team find success. For me, just kind of being a part of this group and watching them -- with some of the things that have gone on -- I think that we've been a pretty resilient group."
Marchand led the Bruins with 29 goals and 69 points, followed by his linemates, Bergeron (23 goals, 25 assists) and Pastrnak (20 goals, 28 assists), with 48 points each. Rask went 15-5-2 with a 2.28 GAA, a .913 save percentage and two shutouts in 24 games. Halak was 9-6-4 with a 2.53 GAA, a .905 save percentage and two shutouts in 19 games (17 starts). Swayman was 7-3-0 with a 1.50 GAA, a .945 save percentage and two shutouts in nine games. Vladar was 2-2-1 with a 3.40 GAA and an .886 save percentage in five games.
Backstrom said that the addition of forward Taylor Hall before the 2021 NHL Trade Deadline makes the Bruins more difficult to defend because he adds quality scoring depth behind the top line of Marchand, Bergeron and Pastrnak.
"I think they've proved they have good depth too," Backstrom said. "Obviously that line is very special and they're good but they have other players too that are good. So do we, so I think it's going to be a fun matchup and it's a good challenge for us. They've been so good for many years so it'll be fun. I think we should look at it like a challenge we have to overcome. We finished before them and we've got the home ice and we've really got to take advantage of that, I think."
This will be the fourth playoff series between Boston and Washington. The Capitals won two of the first three, including the most recent, in seven games in the 2012 Eastern Conference First Round.
The Capitals, who qualified for the playoffs for a seventh straight season, lost to the Islanders in five games in the Eastern Conference First Round last season.
The Bruins, who qualified for a fifth straight season, lost to the Tampa Bay Lightning in five games in the Eastern Conference Second Round last season.
The series winner will play the winner of the series between the Pittsburgh Penguins (No. 1) and Islanders (No. 4) in the second round.
NHL.com independent correspondents Matt Kalman and Harvey Valentine contributed to this report