There are bands you passively enjoy, and then there are those whose music, for whatever reason, fits like key to lock in that musical sweet spot deep within your brain. Heartless Bastards have always been the latter type of band for me, and I don’t know whether it’s their gritty Southern influences, lead singer Erika Wennerstrom’s bluesy alto, or some mysterious combination of the two, but I’ve been proselytizing them to the world since I first heard their music.

Apparently, the world doesn’t listen to me, because there were still tickets left unsold for the band’s performance last Saturday at the Casbah. Based on the crowd they drew from thin air at a music festival the last time I saw them, I had just assumed they would sell out — and I found myself wondering, why is this band not huge? Or at least approaching the fame of their fellow Ohioans, label mates — and musical soulmates — The Black Keys? In any case, my fellow fans and I put these questions on hold for the night and just appreciated having them all to ourselves at the intimate Casbah, and with a little elbow room.

The tender piano and vocals of “Into the Open,” from sophomore album All This Time, were a deceptively quiet way to open the show. In short order, though, drummer Dave Colvin filled in with rolling snares, bassist Jesse Ebaugh and guitarist Mark Nathan dropped some soupy rock chords on top, and there was no mistaking it — we were with the Heartless Bastards. When it was over, Wennerstrom wrapped her snakeskin guitar strap around her shoulders, set her piano aside, and tore into “Out at Sea,” a more characteristic, blistering rocker from their latest effort, The Mountain.

Live, the Bastards (may I call you the Bastards?) gave us a few different tastes, from the Cat-Power-esque “Into the Open” to the pure blues of Buddy Guy cover “Done Got Old” to the rich folk interlude of “So Quiet,” which was rounded out by down-home banjo and fiddle. They’re at their best, though, when they stick to their essence — bare-bones but catchy garage chord progressions and simple melodies taken to soaring heights by Wennerstrom’s throaty vocals. A typical Heartless Bastards hit usually has about four or five hooks. The verse is a hook, and the chorus is a hook. Then the bridge is hooky. Bridge #2: also a hook — and they’re even stickier live. I was whistling along to a medley of short loops in my brain from the time I left Saturday’s show until well into the work week.

Behind cropped blonde bangs, Wennerstrom was magnetic to watch, and her band went well with a Saturday night buzz. I wanted to turn around and toast the entire audience when Nathan, stonefaced and stoic, would stalk the stage and hold his axe out at arm’s length for a riff. Likewise, Ebaugh, looking like an NPR-listening rock geek in his rainbow-striped shirt, pulled off his glasses and let loose once the show started. The crowd was moving, and by the encore — stuffed with hits like “Gray,” “Searching for A Ghost,” and “Runnin” — it had become a dance party. When Heartless Bastards were playing, even the obnoxious guy up front casting his lanky arm around like a fishing pole became more hilarious than irritating. What higher praise can I give than that?