It might be down to three.

But there is no question about No. 1.

While Jonas Gustavsson and Jeremy Smith battle for backup goaltender spot, Tuukka Rask stands alone as the most important cog for a bounce-back season for the Boston Bruins.

As Tuukka goes, so likely will the Bruins, beginning next Thursday night when it starts for real in the 2015-16 opener against the Winnipeg Jets.

“I think he’s our number one goalie,” Claude Julien said after Rask’s first start of the preseason Monday night. “We’re not here to evaluate him, we’re here to evaluate the others. For him, it’s to find his groove.”

Monday night was Rask’s first tune-up in the back end of a head-to-head matchup with the Red Wings; his first move to find the groove. And with a young and depleted defense in front of him.

“I think we’re evaluating more the back end than Tuukka,” Julien said postgame about a preseason team focus on the defensemen.

Last year, the 2013-14 Vezina Trophy winner put in a workhorse effort that came up two points shy of extending the regular season. In 70 games – 67 starts – Rask went 34-21-14 with three shutouts, a 2.30 GAA and a .922 save percentage.

Rask’s first save of this season came five minutes into the game that featured a Bruins lineup looking more like opening night than any thus far. Detroit went on the power play at 14:07 after five shots were turned aside by Rask. One Tomas Tater laser to Rask’s right was all the Wings could muster, and the period ended with Rask and Jimmy Howard each posting a 5-save stat. That period may well portend the goal this entire season: hard-nosed team defense — and Rask pitching goose eggs in low-scoring outcomes.

With less than a minute left on a Bruins’ power play early in the second, Ryan Spooner clanged the crossbar behind Howard; two minutes later Loui Eriksson was denied by the former University of Maine standout on a clean break-in.

At 7:11 that team defense would break down when a wide-open Drew Miller — left unattended in the right faceoff circle — promptly wristed one over Rask’s right shoulder for a 1-0 lead. Ditto at 10:34 when Tomas Jurco took a pass in the neutral zone, and streaked half the rink before pasting Rask with another wrister for the 2-0 lead.

“The timing was sometimes a little off and angles were a little off; not natural all the time,” Rask assessed postgame about the first two goals.

Through two periods: 16 total shots on Rask and his teammates 0-for-3 in prime scoring opportunities with only 14 shots for Boston.

Jurco would dribble one past Rask 48 ticks into the third en route to a 3-1 final with Rask saving 21 of 24 total shots. Howard denying Ryan Spooner, Brad Marchand and Patrice Bergeron of primo final frame scoring opportunities before Julien pulled Rask with three minutes left.

A 6-on-4 with a minute to go, put Eriksson on Howard’s doorstep for Boston’s only tally, denying the shutout at 19:09.

“You forget how tough it is out there,” Rask said. “No matter how much you work out, it’s always different in a real game. I definitely felt it.”

Not the kind of game the Bruins want a week hence when two points are on the line for 82 contests.

“Some of those shots were really top shelf,” Julien said about his stellar netminder. “They were good goals. It’s his first game so like anybody else he’s entitled to have those games. It wasn’t a bad game on his part at all. First game and no doubt he’ll feel even better in the next one that he plays.”

Removing rust is one major reason why they play a preseason.

“Good to get it out of the way,” Rask said. “It’s good to get that first one under the belt and keep moving on. At this point, I just focus on myself and getting my game where I feel like it needs to be.”

When asked how long it takes for his game to click, Rask said: “Hopefully not more than two.”

The Bruins play two more preseason games before the opener on October 8 when the Rask task begins.