I’d reckon that a vast majority of the throngs that filled the seats and lawn of Xfinity Center for Monday’s show featuring Green Day would give you a top shelf Keanu Reeves blank stare if you mention Neurosis. The long-running Bay Area sludge/metal band just played Boston three weeks ago, and at the start of their career sharing the stage with Green Day at the hallowed all-ages mecca of Gilman Street was a routine occurrence. Since then, their respective trajectories have departed sharply; who could have foreseen that Dookie would irrevocably change Green Day’s fate in such a drastic manner?

Playing the Boston area for the third time in less than a year hasn’t dampened enthusiasm for the trio’s brash and irreverent take on punk/pop rock, and while the stage show and set list stayed pretty much on course with the previous two shows, the mix of younger and older fans didn’t mind in the least; this was one of the more actively engaged audiences I’ve seen all year. And Billie Joe Armstrong didn’t fail to stoke that engagement with the audience, a few lucky ones much more directly than others.

As in previous shows, he recruited a fan to shout out a line of “Know Your Enemy” before launching off the stage and back into the audience (directly over my head, as it turned out), a lucky kid showing punk rock history knowledge via his Agent Orange t shirt got to bang out some chords on a cover of Operation Ivy’s “Knowledge,” and what looked to be a five year old kid did the honors of singing “Longview” when Armstrong claimed he forgot the words. I was wondering what sort of situation was gonna happen when he arrived at the “When masturbation’s lost its fun/You’re fucking lonely” line, but he didn’t appear to know the first taboo word and Armstrong took the mic away on the second lest he be blamed for abetting the profanity of a pre-schooler.

Despite the years logged doing this, the band always looks like they are having the time of their life. Tré Cool still has the firecracker drum fills down pat on 1992’s “2000 Light Years Away” and keeps things on very sure footing. Mike Dirnt looks like he swapped piña coladas for coconut water years ago, constantly on the prowl and throwing jump kicks in on a regular basis.  For “American Idiot,” the Gibson that Armstrong chose to play was scored deeply down into the wood from routine downstrokes coming in early, and that’s an apt metaphor for the band. They might be showing some effects of being in this game for so long, but they’re still firing on all cylinders and appealing to every new generation of teenagers that keeps filling the ranks.

Welsh rockers Catfish and the Bottlemen drew opening act honors, and while they were pros at acing the rock moves on stage, the sound mix was pretty atrocious and it was hard to differentiate them from the Kooks/Band Of Skulls/Kasabian-type UK rock bands of the moment.

For more photos of both bands, click on the slideshow: