Dropkick Murphys made their first Summerfest appearance Friday night and it's not a reach to say it won't be their last.

The Boston-based Celtic punk outfit, which has developed a devoted local following with frequent visits and sweat-drenched shows in tiny clubs all the way up to the Eagles Ballroom, played an energetic 90-minute set before a jam-packed house at the Harley-Davidson Roadhouse.

"Now we know what we've been missing," said bass player Ken Casey, a founding member of the 13-year-old group that champions the working class and also has served as something of an unofficial house band for the Red Sox, Bruins and Celtics.

The Dropkicks are so huge in Boston that their annual St. Patrick's Day show is a must-attend event. When Bruce Springsteen played Boston in April, he invited the Dropkicks to join him for "Glory Days" and "American Land" and allowed guitarist / accordion player Tim Brennan to propose to his girlfriend on the stage, following the act with a version of the rare "So Young and In Love."

A few weeks ago, Aerosmith played a "Hometown Heroes" concert at Comcast Arena in Mansfield, Mass., and invited the Dropkicks to open. "I've always wanted to see them live," guitar player Joe Perry told a local paper. Aerosmith invited the Dropkicks onstage to play the Boston anthem "Dirty Water."

Anyone who witnessed the show Friday could see that the Dropkicks' appeal is not limited to places where clam chowder doesn't come from a can. This is a group that grabs its audience by the lapels from the opening notes and doesn't let go.

The setlist was filled with favorites, from "Barroom Heroes" and "Flannigan's Ball," to the poppy "Sunshine Highway," "Forever" and the classic "Kiss Me, I'm *hitfaced," which deviated from the norm because it was performed without all the female attendees on stage.

Casey, an avid golfer who teed it up at a local course Friday afternoon, gave a shout-out to the guys at "the Duke Roufus gym" and he and the band rocked to a crescendo with an encore that featured a fist-pumping version of The Who's "Baba O'Reilly."

It was the final song of the night, "I'm Shipping Up To Boston," where the show took a turn from impressive to epic. The song, which serves as a theme for Red Sox closer Jonathan Papelbon in the way "Hell's Bells" revs up fans Brewers veteran Trevor Hoffman, features the lyric:

"I'm a sailor peg
And I've lost my leg
Climbing up the top sails
I lost my leg!"

During the song, a young male fan with a prosthetic leg jumped on stage, danced, and then removed his leg and waved it around as he hopped to the churning beat.

As the fan enjoyed a post-show beer backstage and collected autographs on this prosthetic, someone asked Casey when the last time such an incident occurred.

"It was last night (in Grand Rapids)," he said. "But, this guy had better stamina. The guy last night jumped around for about 30 seconds and he got tired and sat on the drum riser. This guy had better stamina."

Stamina wasn't a problem for the Dropkicks and their fans, who kept the merchandise tent and beer tents busy before, during and after the show -- a strong sign that they'll be back for Summerfest 2010.