Any of Bill Callahan’s diehard fans can spout their favorite line from the enigmatic singer-songwriter’s catalog (my current favorite, from “Rococo Zephyr”: “I used to be sort of blind / Now I can sort of see.”) Callahan’s early work as Smog features little else than this terse wordplay delivered in his glassy baritone, leaving bewildered listeners to parse through his metaphors and non sequitars with the occasional blast of noise.

Monday night’s show at the spacious Oriental Theater may have come as a shock to those living under a rock for the past decade of Callahan’s critically-adored career. Ever since making the switch to his own name as a performer, the 20-plus  year veteran of indie music has been diverging from his jarring early work by broadening his sound into a gorgeous, plaintive, and hi-fidelity indie folk sound.

Backed by three musicians (plus opener Howling Hex’s guitarist for the cover of the Velvet Underground’s “White Light/White Heat”) Callahan stuck mostly to material from his past three albums, including this year’s wistful Dream River.

Callahan surprised the crowd with his ability to extend songs like “Ride My Arrow” and “One Fine Morning” past their standard running times, and even turned out a twitchy guitar solo on a 10 minute cover of Percy Mayfield’s “Please Send Me Someone to Love.” He was also gracious enough to close with an audience member’s request for “Sycamore,” dispelling any notions of the artist’s aloofness.

The evening’s highlights came from 2011’s Apocalypse. His feisty rendition of “America!” showcased Callahan at his most jovial, a harmonica wrapped around his neck to toot along to killer lines like “I watch David Letterman in Australia!” The singer was the only band member standing during the performance, and tracks like the aforementioned ditty and the relatively more rocking “Drover” found Callahan grooving along. I probably wasn’t the only member of the audience who never thought he would see the nearly-50 Callahan dancing. But there he was, hips and legs swaying back and forth -- and we couldn’t help but do the same.