Backstrom had four shots on goal and won 6 of 9 faceoffs, but the Capitals fell to Tampa Bay 4-2. With the win, the Lightning evened the series 2-2.
Backstrom was a game-time decision Thursday morning before being medically cleared to play.
"It's the playoffs,'' Backstrom said after the game. "You've just got to grind. It felt good on the first couple faceoffs, so I just kept taking them.''
Backstrom had missed the previous four playoff games after taking a shot off the hand from Pittsburgh defenseman Justin Schultz on May 5.
"I should get back to normal,'' Backstrom said after playing 18 minutes, 51 seconds in his return. "I feel really good. I don't know [how normal] exactly. If I didn't feel good, I wouldn't play. The doctors wouldn't let me play, either.''
He had participated in the morning skates for Washington this week but returned to taking line rushes and power-play practice time only on Thursday. He had been wearing a brace on his right hand.
A hard-luck loss included two penalties by fill-in No. 2 center Lars Eller, who has five penalties in the past two games. Coach Barry Trotz didn't mess with his top two lines, but Backstrom could easily be promoted to skate with Jakub Vrana and T.J. Oshie in Game 5.
"We're going to need him pushing forward, especially now that he has a game under him,'' goaltender Braden Holtby said. "He'll take on more minutes and a bigger role. You could tell as the game went on he was getting more and more comfortable, so he's going to be a much-needed asset for us in these next few games, for sure.''
Backstrom appears ready to do that.
The 30-year-old Swedish center said that if it been up to him, he would have been back much sooner.
"Nick has been champing at the bit for a while now,'' said Trotz, lauding Backstrom's game. "We've been holding him back a little bit, but he's ready to go.''
Even on a team featuring Alex Ovechkin, Backstrom has been integral to the Capitals' success for the better part of a decade. He's the second-longest-tenured player on the team, and this was his first career game in the conference finals.
"As a hockey player, you want to play,'' Backstrom said. "It feels nice to be back.''
ESPN's Greg Wyshynski and The Associated Press contributed to this report.