Ovechkin was shaken up by a hip check from Maple Leafs forward Nazem Kadri and had to be helped off the ice with 2:28 remaining in the first period. Ovechkin returned at the start of the second period played 19:29 in the game, but it was a scary moment at the time.
"I just needed a little break," Ovechkin said.
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Ovechkin chipped the puck past Kadri at the right point as he was trying to exit the Capitals zone, and Kadri crouched and appeared to make contact with Ovechkin's left knee with his left hip, flipping Ovechkin.
"I thought he got rid of the puck and I just tried to get a piece of him and he tried to get out of the way," Kadri said. "It's not like I stuck my knee out or got my arms high or anything like that. It happened pretty quick."
Ovechkin tried to get up but dropped back to the ice and grabbed his left knee. He put no weight on his left leg when he was helped off the ice by teammates Nate Schmidt and Nicklas Backstrom.
After reaching the tunnel to the locker room, Ovechkin walked the last few steps with a noticeable limp. But Capitals goaltender Braden Holtby said he was confident Ovechkin would be back.
"You could tell on his face," Holtby said. "He still had his game face on."
Williams said, "Ovi's a horse. It takes a lot to hurt that guy, especially this time of year."
Kadri received a two-minute tripping penalty on the play, and T.J Oshie scored on the power play 43 seconds later to give Washington a 1-0 lead.
"[Washington] probably thought it should have been a major (penalty), and I thought there should have been no penalty," Toronto coach Mike Babcock said. "That's the beauty of the playoffs."
Ovechkin said he was watching TV in the locker room when Oshie scored.
"Just have a Coke and enjoy the match," Ovechkin said. "It doesn't hurt. Nothing. I just take the time to watch the power play."
Ovechkin downplayed whether he was upset by the hit.
"It's the playoffs," he said. "I didn't watch the replay, but if it's dirty it's dirty. The League is going watch it, and if not, it doesn't matter right now."
When the Capitals returned to start the second period, Ovechkin was the last player out of the locker room and the fans started chants of "Ovi! Ovi!" when they saw he was back.
"Obviously it's big momentum for us," Ovechkin said. "Our fans are the best fans in the League. They support us, and you can see everybody was in the game. Sometimes you come into the building and nothing happens, but they are in. They're our sixth player out there."
Ovechkin started the second period by delivering a hit on Maple Leafs defenseman Jake Gardiner in the right corner of the Toronto end.
"I was hoping he's OK," Kadri said of Ovechkin. "It's a pretty tender area. That can be extensive. You don't want that to be an extended injury. Glad he came back. He was running around a little bit when he came back, so he must have been fine."
Game 6 is at Toronto on Sunday (7 p.m. ET; NBCSN, SN, TVA Sports, CSN-DC).