IT’S hard enough to be a saint in the city, let alone live up to godlike status, but guitarist Eric Clapton was back on Mount Olympus at his one-night benefit concert for his Crossroads drug rehab center.

The show at Madison Square Garden Wednesday was billed as “Eric Clapton and Friends.” Sheryl Crow and Mary J. Blige signed in early, but it was a late-show visit by Bob Dylan that turned another variety program into one of the summer’s most memorable music events.

Most concerts squeeze in 17 to 20 songs before bringing the curtain down. At this show, squeaky-clean-‘n’-sober Clapton sizzled for 24 songs before Dylan even got near the stage.

When he did it became one of those rare moments in music when legends flex their muscles and prove why they’re still the big dogs in the yard.

Clapton, the Englishman, looked dapper in a dark suit and played a new black Fender Stratocaster guitar (having just auctioned 100 of his old guitars, raising $5 million for the rehab center). American-made Dylan donned one of his signature black bandito outfits with an ax that matched Eric’s.

The men, backed by Clapton’s 10-piece band, cut heads with flashy blues licks that would have stirred Muddy Waters. Their bit together opened with Dylan doing a wounded-dog vocal on his famed “Don’t Think Twice.” He croaked, Clapton smiled and even grimaced a little, and then suddenly Dylan cleared his pipes and his head and nailed the next six songs, hitting his stride on the deep blues of “Leopard-Skin Pill-Box Hat.”

Those at this three-hour-plus concert witnessed the kind of performance it takes to humble a guitar guru of Clapton’s stature. Clapton stepped back from the mike at center stage to make room for Dylan. He and Bob did their best work on the song “Crossroads,” where they were all smiles, as if they each knew the other was in top form.

Leading up to that concert zenith was a series of major peaks and a few minor valleys. The show started with Clapton doing a pretty fair blues set that included originals like the opener “My Father’s Eyes” and blues classics like “Hoochie Coochie Man.”

All of which was OK, but it was a predominantly slow blues set that was nice to listen to but hardly made the blood boil.

Then Crow joined Clapton to play what was a mini-concert of her greatest hits. She was in good voice, but the sound person had her miked so loudly that on songs like “If It Makes You Happy” (in which the chorus is shouted) her volume hurt your ears.

Even though her too-powerful vocal mix was not corrected during her set with Clapton, Crow was still one of the fan favorites. Her portion of the show was best during a duet with Clapton on a cover of the late Jimi Hendrix’s “Little Wing.”

R&B queen Mary J. Blige didn’t fare as well with the decidedly older crowd at the sold-out Garden. In a show that seemed like classic-rock radio come to life, she was out of place. One fan nearby actually read a newspaper during Blige’s segment, which was nonetheless really very good.

In her tight jeans, fluffy vest and feathered cowboy hat, Blige ripped through a fantastic, funk-powered version of “You Are Everything,” but for some reason she never touched this crowd, never took command of the Garden. That doesn’t happen very often to Blige. She left the stage after half a dozen songs in a noticeable huff.

Even with its flaws, this was the best Clapton show in 10 years. The man played hard, he infused his beloved blues with enough rock to excite not only the fans but the band, too. He even ditched the sappy, slow acoustic arrangement of “Layla” and played it like a rock song, like it was written.

The show will be broadcast on VH1 July 17. The cable station gets points for bringing a concert like this to a wide TV audience, but VH1 was also the night’s big party pooper.

The station, whose motto is “The music first,” became the punch line to all the jokes about what’s wrong with rock ‘n’ roll, as its uptight camera crew in my section actually got pushy with fans, telling them to stop dancing because it made the camera jiggle, and to sit down so the crew could get a clear shot.