There are plenty of reasons Fun. would want to open Friday's sold-out Orpheum show with “Out on the Town.” For starters, there were the pealing guitar arpeggios and proclamatory drum pounding that set the anthemic tone of the night. But there was a line that singer Nate Ruess kept repeating toward the end that was maybe more important: “Open up your heart.” Despite the infuriatingly cutesy, copy-editor-defying way its name is formatted, there was almost nothing cynical about the band.

That’s a hard trick under the best of conditions in the modern musical landscape. For a band that relies heavily on both Queen-ly anthems and a distinct late-’70s pop sensibility that comes out most often in roller-rink keyboards, it’s practically a high-wire act. But there wasn’t a smirk in evidence during the fist-in-the-air shuffle of “Carry On,” the jackbooted march of joy that was “Some Nights,” or the Supertramp-like “All the Pretty Girls.” When Ruess jumped up and down and clapped in time — something he did quite often — it wasn’t an ironic commentary on enthusiasm. He meant it.