Pogues’ MacGowan parties on

A Pogues show is a perverse pleasure. While seven members safely sipped bottled water through Thursday’s raucous Avalon show - the first of a four-night Boston run - frontman Shane MacGowan continued his slump toward ruin with his fans toasting his decline.

MacGowan is the only one of the reunited Pogues still wrecked. He opened the show with a bottle at his feet, a pint on the stool at his side, and a cigarette in hand. Diving in with fan favorites “Streams of Whiskey” and “If I Should Fall from the Grace of God,” MacGowan’s powerful and poetic lyrics were slurred (even more than usual), but his trademark raise-the-roof shouts and screams were as glorious as ever.

Behind him the band was dressed like respectable Irish gents, but its playing belied the coats and ties. Accordion player James Fearnley promised the band’s sobriety wouldn’t damper its ramshackle force, and he made good on his promise. Fearnley stumbled around the stage like a man possessed, dancing and yelling and leaping off the drum risers like Pete Townshend with a 25-pound squeezebox.

And it’s a good thing the band is still so spry: As he ages, MacGowan relies on his mates more than ever. After singing a few tunes MacGowan shuffled off stage and cittern player Terry Woods led those remaining through an earnest “Young Ned of the Hill.” Throughout the night this pattern repeated itself. MacGowan would disappear, another Pogue would sing a tune, and MacGowan would re-emerge with a fresh cigarette and drink.

Sadly, it’s MacGowan’s carousing that defines a Pogues show. No one seems to care if tin whistler Spider Stacy has traded whiskey for Dasani, but, as the unmistakable focal point, MacGowan needs to be a mess. The crowd has come to expect it and spent much of the show shouting “Shane” and raising cans of Guinness and plastic cups of Jameson in his honor. And, while the slurring makes it harder to understand the lyrics, it also imbues many songs - notably “Dirty Old Town,” “Bottle of Smoke” and “The Sickbed of Cuchulaim” - ith a poignant authenticity.

The distressing irony is that with the band in tiptop shape and MacGowan descending further into a magnificent, magnetic caricature, the chances of another reunion decrease as their leader slips further away.

Not everyone was sold on the Pogues’ legendary Irish folk punk. While most of the crowd huddled close to the stage singing along with every lyric, at least a third hit the doors early.

Maybe MacGowan’s performance couldn’t keep them engaged or maybe it was the weeknight and the cold, but many left before the final encore, the last-call party anthem “Fiesta.”