The Bruins have no alternative but to try to put as positive a spin as possible on an abbreviated regular season during which the team underachieved — rarely delivering a truly complete 60-minute performance.

The basis of that spin in advance of tomorrow night’s Eastern Conference quarterfinal series opener vs. the Toronto Maple Leafs at the Garden: Don’t judge us on the first 31⁄2 months of mediocre play — yes, even during that misleading 17-3-3 start — but on the final three games of the regular season.

Even though the B’s were just 1-1-1 in those games, they finally showed hints of effort and grit and cohesion, nothing sensational, mind you, but at least small improvements on the earlier sloppy and half-hearted efforts.

That was the message from general manager Peter Chiarelli during a conference call with reporters yesterday. The GM was candid and critical of the B’s season, yet hopeful his team may be ready to upgrade its play in the nick of time.

“If I’m going to judge our team on the last half of the season, I’m going to say we really have to step up our performance to have success in the playoffs,” Chiarelli said of a team that went 11-11-3 over the final 25 games. “We certainly haven’t been firing on all cylinders. In the last three games I’ve liked the physicality. I’ve liked the effort. It’s been consistent. We are starting to generate more chances. We’re not finishing the chances — we have to improve on that — but we’re generating more chances. So the level of activity and intensity has picked up. That, I like.

“The message (for the team): I want that to continue. Eventually we’ll find our game and our execution and our skill level. We’ll find it if this other stuff is in place.”