Playing for the first time since May 1, Samsonov made 40 saves, including 17 in the first overtime. He had been on the taxi squad and was removed from NHL COVID-19 protocol Saturday.
"He played a heck of a game, and I talked to him about that first and foremost," Capitals coach Peter Laviolette said. "The miscommunication, there's two people involved there. The communication's got to be better. I think one person was thinking one thing and it seemed like a pretty harmless play, and it ended up poorly."
Samsonov said some of his teammates tried to lift his spirits.
"Everybody helped with me in the locker room, coaches, everybody," he said. "The game is much easier when you get the support."
Samsonov and center Evgeny Kuznetsov were scratched for a 6-3 win against the New York Rangers on May 3 for disciplinary reasons. Kuznetsov was placed into NHL COVID-19 protocol the next day.
Samsonov was 13-4-1 with a 2.69 goals-against average, a .902 save percentage and two shutouts in 19 games (18 starts) during the regular season and was competing to be Washington's playoff starter. Rookie goalie Vitek Vanecek started Game 1 but sustained a lower-body injury in the first period of a 3-2 overtime win.
Craig Anderson made 21 saves on 22 shots in relief of Vanecek in Game 1 and then started and made 44 saves in a 4-3 overtime loss in Game 2. Anderson, who turns 40 on Friday, was held out of Game 3 because of what the Capitals called "body maintenance."
"Maybe a couple days ago I felt good," Samsonov said. "I'm ready for everything."
Kuznetsov, who confirmed he tested positive for COVID-19 for the second time this season, was removed from protocol Sunday. He had one shot in 26:41 of ice time in Game 3 as the center on a line with Alex Ovechkin and T.J. Oshie.
"It's nice to be back and right away to playoff hockey," Kuznetsov said. "It's always fun. It's all we've been dreaming about and, of course, it wasn't easy, but I believe that for everybody it's not easy."
Kuznetsov has scored 62 points (27 goals, 35 assists) in 79 playoff games, including an NHL-high 32 points (12 goals, 20 assists) in 24 games when Washington won the Stanley Cup in 2018. The Capitals scored eight goals in the first three games against the Bruins.
Neither team has led by more than one goal, and each game has required overtime.
"It's a tight series. It's close," Laviolette said. "The difference is small. We've got to find a way to bring that difference to our side tomorrow.
"We're going to need to generate more. So we're going to count on the top players, including [Kuznetsov], to make that difference and impact in the offensive zone. It was good to have him back out there. It gave us a natural centerman, and jumping into a train that's moving pretty fast and all that, I thought he did a pretty good job."