Officially, there hasn't been a Grateful Dead concert since 1995, when the musical entity with that name dissolved following guitarist Jerry Garcia’s death. But try telling that to the fans filling baseball stadiums and sheds this summer to see most of the surviving members under the banner of Dead & Company, most lately for two shows this past weekend at Boston’s Fenway Park. Riding yet another wave of popularity following the band’s 50th anniversary last year, the Dead’s 21st century crest also comes with a long-term critical reappraisal by the world outside the band’s cosmos-sized Deadhead bubble, lately including the National’s high-profile, big-budget multi-disc Day of the Dead tribute.

Yet for a certain segment of Dead freaks, Dead & Co. presents a conundrum in the form of a lead guitarist: the blues-pop phenom and human GIF John Mayer, the musical and visual opposite of Jerry Garcia in nearly every regard. Where the autodidact Garcia was a model of psychedelic beardo cool (young) and dope-addled Santa Claus inertia (later), Mayer’s Blues Hammer melodrama, flashy stage moves, and fashion awareness make him an odd substitute for Garcia’s black t-shirts and bluegrass delicacy. One satirical Dead-loving site refers to him frequently as “Josh.”

And during their second night at Fenway Park—the closing show for the first leg of the summer’s tour, which included two headlining sets at Bonnaroo—Josh remained an occasionally awkward musical partner for Grateful Dead guitarist Bob Weir and drummers Billy Kreutzmann and Mickey Hart. But, despite this, over two sets and three hours of music, Bro & Co. succeeded at achieving what the Dead did so well (sometimes) and conjured mojo at large scale in the unfriendly confines of a major sporting arena on a muggy summer eve. Lurching into motion in daylight, the sextet jammed slowly into “Truckin’” and were on their way, sounding more like a band than the group featuring Dead bassist Phil Lesh and Phish guitarist Trey Anastasio that played five shows last summer, if less musically adventurous.

Bouncing and grinning and no less silly than any number of other replacement Garcias, Josh brought a youngin’s energy to the stage. With the band’s legendarily hypnocratic touring operation slurped into the empire of Mayer manager (and Eagles mogul) Irving Azoff (with co-management from Grateful Dead rep ROAR), Dead & Co. are likewise the slickest and tightest version of the Dead in years. But, even still, not too slick. Kreutzmann and Hart’s double-drumming was as chaotic as ever, the group’s miscues and ponderous moments as reliable as Bob Weir’s sandals. While the band’s critical revival is built mostly around their creative activities from 1965 to 1977 or so, Dead & Co. most audibly channeled the group’s ’80s incarnations, years when (not coincidentally) Weir and Hart were increasingly centers of the band’s onstage energies as Garcia withdrew into addiction. It is these years, too, that the band was most popular, achieving their only Top 10 hit in 1987 and activating uncountable swaths of new Deadheads.

More than a quarter-century later, Dead & Co. at Fenway Park presented a truly all-ages (if mostly white) spectacle: children in their first tie-dyes, hard-boogeying septuagenarians, spun-out twenty-something tour rats who never got to see Jerry, and unassumingly bopping middle-aged enthusiasts all sharing the joyful space created by the Grateful Dead’s music. It’s hard to think of another tour this summer that’s as friendly to families as it is to psychedelic users. Besides national parks, there aren’t many institutions that serve both. But unlike members of the Grateful Dead, national parks don’t go on tour.