Let's just take this from the top if this is where we actually want to go...
Pretty clean DZ faceoff win. Puck slapped into the corner as designed for Orlov, Niskanen widens out to start out against the flow of Hurricanes. Wilson is fixin' to support that.
Niskanen - who had a rough night - gets a little bit of a bouncing disc and as a result, he can't peel the puck off the boards as clean as he'd like. He finally does last second and fires a pass right to the point where Wilson's stick is meeting the boards - that's a tough place to catch a pass. The puck skips between his stick and his feet as he was a little too quick to go about it. He feels the pressure to get this pass and start transition (in general, but also I imagine Ovechkin is yelling for this puck already), but in a game that was a ping pong match for the better part of the last 45 game minutes, Wilson is not totally safe, and he'll soon be sorry.
Backstrom immediately jumps up to fill the RW role that Wilson would ordinarily fill. Ovechkin has completely flown the zone. Vintage Ovechkin where he'll get a chance to carry the puck through the NZ in a 1 on 1 situation against a defenseman that has positional integrity. That has failed him in the past (Girardi, et al.), this mindset failed him tonight as well...as he played a defenseman's worth of minutes but was not terribly effective outside of causing Dougie Hamilton to fill his diaper (once again) and then an oddly bad play from the remarkable Jaccob Slavin (early Conn Smythe watchlist) to try to cover for Hamilton's very unclean ass.
Meanwhile, back at the ranch...with the LW Ovechkin out of the zone, Slavin puts the puck into the Washington left side/Carolina right side knowing that they'll have a numerical advantage.
Justin Williams, who started the forechecking play off the lost draw by applying pressure to a not overly poised Niskanen, is first on the scene. Like he did all night, he grabbed the puck and threw it at the net. The sides have flipped as a result of the sudden change versus the flow and RW Williams has his shot fronted by RD Niskanen.
Orlov is in the near lane with a stick on a rather non-threatening Sebastian Aho who is really just cruising through to support a cycle play - which given how the night was - that was the expected play. The play that would have developed knowing what I know about Aho and Williams would have resulted in Aho cutting back against the inside of a trailing Orlov and feeding one back on his forehand to the strong side post for Williams to throw over Holtby's glove and win me hundreds of dollars (as I had bet Williams GWG at 14:1)...insteadddddd...
The play happens quick and the inexperienced defensive net front man Tom Wilson only has body positioning, but does not have the industrious Brock McGinn's stick. With an unmolested stick, McGinn is able to win the series for the fairly heavy underdog.
A more experienced support center like Backstrom - though soft as a human with his dad bod, is very handy with his stick positioning as a rule - offensively and defensively, he makes room with subtle stick picks quite often. Whether he would have gotten McGinn's stick we'll never know, but he's a LHS, and likely would have come up on his backside to stick lift in exchange for trying to make a box out play (or some faux version of it) like Slick Willy did...
You can't be too upset with Ovechkin because this is who he is...this isn't new or unexpected behavior. Live by the sword, die by the sword. Like in most of the other playoff failures, Ovechkin cheats to compensate for the lackluster puck carrying ability of Nicklas Backstrom relative to Evgeny Kuznetsov (who was a pumpkin in the series). Savvy observers wondered why all of a sudden the Caps were able to win a series in 2018, well part of it (a huge part of it) is they were able to get away from this exact situation...Kuznetsov could carry pucks across lines in the middle of the rink, Kuzy is a much more balanced offensive player in a more advantageous position...as opposed to most of 13 years of Ovechkin, a RHS, carrying it up the LW without being a terribly strong playmaker as far as elite players go. Limited options there and a player who - as we see - is better served being as a finishing option more than a starting option for plays.
Ovechkin a NZ puck carrier and distributor, Wilson the F1/support center near the net, Backstrom as a winger...players in uncomfortable situations and/or less than ideal conditions don't tend to play at 100% capacity. Thus, they are more prone to fail. It's the anatomy of a goal and a small piece of the anatomical makeup of the larger team concept.