Ovechkin got things started for the Capitals as they went up 1-0 thanks to his power-play goal.
Teammate Anthony Beauvillier followed up by scoring the lone goal of the second period to put the Capitals up 2-0.
In a game that saw over 70 hits and over 120 total shots (70+ on goal), Canadiens' Cole Caufield finally got by Capitals goaltender Logan Thompson in the third period to shorten the lead to 2-1.
Habs teammate Kurt Suzuki tied it all up which sent it to overtime.
And who better to score the game-winner than Ovechkin himself? It marks his very first Stanley Cup Play-offs overtime goal and gave the Caps a 3-2 win.
Winnipeg Jets 2-1 St Louis Blues
Mark Scheifele scored his second goal of the series so far to give the Jets an early 1-0 lead.
But St. Louis Blues' young forward Jimmy Snuggerud sniped one into the top left-hand corner during a power play to tie it all up.
It wasn't until Jets' star Kyle Connor scored his second goal of the series that ended up being all Winnipeg needed to take home back-to-back wins.
While not having as many hits as the last game, the two teams were relatively even on the stat sheet.
Both had 22 shots on goal while the Jets outhit the Blues 33-29. But St. Louis failing to score on their other three power plays proved to be the deciding blow in this matchup.
Los Angeles Kings 6-5 Edmonton Oilers
The Los Angeles Kings claimed victory in a tight battle with the Edmonton Oilers in the first game of the series between the two.
The Kings made the stronger start, going 2-0 up in the first period, and that lead was 4-1 by the start of the third.
However, the Oilers then rallied and levelled things up at 5-5 in the closing stages, but Phillip Danault then fired in a winner for the hosts.
Dallas Stars 4-3 Colorado Avalanche
The series between the Dallas Stars and Colorado Avalanche is now level at 1-1 thanks to the former's 4-3 victory on home turf.
After a tight opening period that ended 1-1, Colorado pulled ahead 3-2 in the second, but the Stars edged the third 1-0 to take the clash into overtime.
There, Colin Blackwell was the hero for Dallas, scoring the winner with just over two minutes to go.