The Avalanche tested their recent invincibility by putting a prospect in the net against a top-five scoring team in the NHL, as if just to show how good they’ve been.

The flex almost worked.

Colorado lost 7-5 to the Devils on Wednesday after digging and almost climbing out of a 5-1 hole in the second period. Alexandar Georgiev, who had started eight of the previous nine games, got the night off before Saturday’s critical divisional tilt at Dallas. In his absence, Justus Annunen’s third career start was a slog with 22 saves on 28 shots faced — though not all the goals were his fault, and he settled in for a clean third period.

Avalanche coach Jared Bednar said he never considered pulling Annunen; this was one of the few remaining chances on the schedule to give Georgiev more than two consecutive days of rest. Plus, it was a good lesson in short-term memory for the young goalie.

“We hung him out to dry way too many chances in the first period,” Bednar said. “There were some saves that I would have liked to see him make, for sure. But he did make a handful of big saves when we were pushing.”

The struggles culminated with sarcastic cheers from the home fans when Annunen stopped the puck during the middle stanza. But a few minutes later, the 22-year-old was denying breakaways and making windmill glove snags, earning back the applause in earnest (if maybe guilty) form.

“Use it as a little boost for training,” an upbeat Annunen told The Post. “You’re not ready yet, so you just need to work harder every day and try to make those saves someday.”

The rapid mood swing in Ball Arena was caused by a burst of three unanswered goals in a span of 2:04 — on four shot attempts (the other hit a post.) Down 5-1 seven minutes into the period, Mikko Rantanen redirected a shot by Josh Manson for his 41st goal. Scoring is often contagious for the Avs, especially their star players. Soon, Nathan MacKinnon was collecting a pass from Bo Byram, dangling around two Devils and taking advantage of Vitek Vanecek’s open five-hole.

Rantanen and MacKinnon have both scored in five consecutive games, combining for 12 of the team’s 23 goals during that stretch.

But on trade deadline week with his job under scrutiny, it was second-line center J.T. Compher who sent the place into mass hysteria another 30 seconds later with a superb individual play on the rush. His top-shelf shot narrowed the gap to 5-4.

Suddenly it was all Avs. Valeri Nichushkin was in the middle of the action, but he skated to the bench with his shoulders sagging at one point after failing to convert a chance. Bednar chose to ride his rookie goalie in the third, and Nichushkin kept chugging along, too. Down 6-4, a Sam Girard shot pinballed off Nichushkin at the net front. The Avalanche kept chasing the lead but couldn’t get the last breakthrough.

Colorado’s slippery start was a smorgasbord of ugly defensive-zone giveaways and poor net protection by Annunen. Newcomers Lars Eller and Jack Johnson teamed up for a blunder along the boards 60 seconds into the game, leading to an Ondrej Palat goal. Manson struggled to defend Annunen’s crease twice during a bad Avalanche shift that ended with a puck stuffed under Annunen’s blocker.

“New Jersey will make it real tough on you with their forwards and their skating ability,” Bednar said. “And their swarm on the puck in all zones. … The part early is we’re checking with our eyes. It’s contain, contain. We’re defending. We’re not checking. So they found too much space too easily.”

Another goal started when MacKinnon couldn’t get a zone-clearing pass through New Jersey sticks. Another started with a Devon Toews turnover along the boards.

It amounted to the kind of sloppy, riveting game that fans love and Bednar typically hates. During a third-period review of Nichushkin’s goal, a young fan swiftly solved a Rubik’s Cube and caused Ball Arena to go bananas. The big screen cut to Nuggets player Bruce Brown several times throughout the comeback, dubbing him the “Rally Bruce.”

But the Avs’ bid at a third four-goal comeback in franchise history was finally halted by a last-minute empty-netter.

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