In regulation, Patrik Elias scored twice and David Clarkson, Jamie Langenbrunner and Brian Gionta added goals as New Jersey gained a split of the home-and-home series following the Capitals 3-1 win on Friday night in Washington.
Ovechkin sent the game into overtime with his second goal of the game, coming with a second remaining in regulation. In a wild goalmouth scramble, the puck came right to Ovechkin, who was all alone to the left of the wide-open Devils net. He slammed the puck home before racing to Capitals' bench for a raucous celebration.
A video review confirmed that the puck crossed the goal line before time expired.
Washington's five-game winning streak came to an end. The Capitals also got goals from Tomas Fleischmann Viktor Kozlov and Nicklas Backstrom, who had four assists.
Washington led 2-1 after one on goals by Fleischmann and Ovechkin.
After Clarkson staked New Jersey to the lead 1:09 into the game, Fleischmann rifled a power-play goal from the right dot past Clemmensen at 6:59.
Ovechkin extended his goal-scoring streak to four with just under a minute left, deflecting Tyler Sloan's point shot.
In the second, Kozlov scored with 3:17 remaining to knot the game at 3 after Langenbrunner and Elias gave the Devils the lead.
Langenbrunner pulled New Jersey even with a shot from the high slot 41 second into the period. Elias put New Jersey up 3-2, poking in a power-play goal at 3:27. Theodore was slow to get up after the score following a collision with Travis Zajac who was crosschecked into the crease by Washington defenseman Brooks Laich.
Theodore shook it off, making a brilliant stop later the period on Parise's wraparound attempt. Theodore dove across the goalmouth, sticking away Parise's bid.
Kozlov then provided the equalizer following a faceoff stalemate between John Madden and Backstrom in the right circle. The puck barely budged, allowing Kozlov to alertly step in and drill a shot past Clemmensen.
The teams traded goals in the third with Elias giving the Devils a 4-3 lead at 6:06 only to have Backstrom pull the Capitals even at 8:11. Gionta scored for the Devils at 11:40, a goal that looked like the winner until Ovechkin connected as time expired.
Washington played without NHL scoring leader Alexander Semin. He missed the third period Friday with an undisclosed upper-body injury.