New Jersey will play the Atlantic Division winner, either the Tampa Bay Lightning or Boston Bruins, in the first round. Boston will win the division with a win against the Florida Panthers on Sunday.
Ovechkin is in line to win his seventh Maurice "Rocket" Richard Trophy as the leading goal-scorer in the NHL. He finished with a game-high eight shots on goal and pushed hard for the hat trick to reach 50 goals.
"Of course it's nice. Of course the end of the season you pay attention to that," Ovechkin said. "Of course you don't want to lose [50] because you have a pretty good chance, but I'm pretty sure right now for us [the] most important thing is the playoffs."
Ovechkin gave Washington a 1-0 lead at 2:21 of the first period when he scored off a cross-ice pass from Evgeny Kuznetsov.
Devils rookie forward Nico Hischier scored his 20th goal at 8:10 of the first period to tie it 1-1 on a feed from Maroon from behind the net.
Nicklas Backstrom gave the Capitals a 2-1 lead with 28 seconds left in the first when he scored off a Brett Connolly pass in front. Michal Kempny scored at 3:44 of the second to extend the lead to 3-1.
Miles Wood scored with 53 seconds left in the second to cut the Capitals lead to 3-2, and Maroon tied it 3-3 at 2:04 of the third.
Ovechkin scored his second goal of the night at 5:11 of the third to make it 4-3, and Andre Burakovsky made it 5-3 at 11:50.
The Capitals spent the final minutes of the game trying to get Ovechkin to 50 goals. They had two late power plays, and Ovechkin was on the ice for 6:04 of the final 8:10.
"We looked for [Ovechkin] a little bit more than usually," Kuznetsov said. "I don't think he's sad about he didn't get 50, but 49 is still a good number."