Any band that can hold a weekly gig for 15 years should be commended. Sabertooth’s decade-and-a-half stint goes down every Saturday from midnight to 5 a.m. at Chicago’s Green Mill. It’s encouraging to hear that jazz’s after-hours image lives on and that, from the sound of the crowd on Dr. Midnight, the band has an audience that wants organ jazz during those twilight hours. Sabertooth’s music moves through a number of familiar settings, but the group’s approach keeps it original. Tenor saxophonists Cameron Pfiffner and Pat Mallinger are the main focus of the band, although organist Pete Benson and drummer Ted Sirota do more than shape the rhythm. The novelty of “It’s Surely Gonna Flop If It Ain’t Got That Bop” doesn’t extend beyond the title. Pfiffner and Mallinger, here on alto and soprano, respectively, rip through some “Rhythm” changes and Benson eschews standard B3 tricks in favor of rapid lines. Their take on the theme from The Odd Couple inspires Mallinger to shout and wail through his horn; by the time Mallinger takes his solo, visions of Felix and Oscar are long gone. In between, the group presents its version of the blues, reinvents a calypso number and gives the Grateful Dead’s “China Cat Sunflower” a second-line beat.