Despite being on a “never-ending tour,” Bob Dylan does not cease to be reliably unpredictable live. Dylan, along with openers Elvis Costello and Amos Lee, performed at the Cumberland County Civic Center in Portland last Thursday to an almost sell-out crowd, full of baby boomers, as well as plenty of 20- and 30-somethings. It’s a testament to his enduring popularity that Dylan can attract multiple age groups to his concerts.

Kicking off the show with a rockin’ version of “Leopard Skin Pill Box Hat,” Dylan then segued into a gently reworked rendition of “Don’t Think Twice, It’s Alright.” In fact, Dylan’s early folk days were well-represented, including “Chimes of Freedom” and the continually relevant “Masters of War.”

The most prevalent Dylan era, though, was his newer stuff. He played six songs from “Modern Times,” a few of which, like “Workingman Blues,” dragged on a little too long and lost the audience’s attention. Lively, nimble songs, however, like the romantic “Spirit on the Water” and the jaunty “Thunder on the Mountain” brought the energy level back up.

Dylan, looking every bit the riverboat gambler in his black boots and wide brim western hat, stuck almost exclusively to the keyboard, only playing guitar on the first three songs. His band, dressed in gray suits and hats, shuffled instruments easily, and took cues from their bandleader as they jumped into at-first unrecognizable versions of “Tangled Up in Blue” and “All Along the Watchtower.”

When you spend over half the year on the road, and you’re Bob Dylan, it only makes sense to change and rework your music. They may be integral parts of contemporary American culture, but they’re still songs, which means they’re living, breathing things. I’d expect nothing less from someone as mercurial as Dylan.

Elvis Costello, himself a bit of a legend, played an acoustic set to open, charming the crowd with lots of witty anecdotes and filling the arena with his voice. One thing people sometimes forget with Elvis Costello is that he’s really got quite a powerful set of pipes, showcased nicely on classics like “(What’s So Funny ‘Bout) Peace, Love and Understanding,” and “Veronica.”

Costello also previewed two brand new songs, the names of which I missed, but one of which he told the audience was written for a new album for Loretta Lynn. Like Dylan, Elvis Costello has a wide, eclectic catalog of songs to choose from, with a body of work rivaled by few. To see two such formidable songwriters share a stage was truly a treat.