Fantasy became reality for some Milwaukee rock and roll fans Wednesday night when Akron's finest, The Black Keys, played the Marcus Amphitheater.

When the show was announced in late February, it took some Milwaukee music fans by surprise.

"If you ask me," I wrote then, "this is one of the most exciting main stage announcements Summerfest has made in a long time."

I also wondered if the more accessible sound of the most recent outing, "Brothers" -- which earned the band three Grammys this year -- had succeeded in building an audience vast enough to allow The Black Keys to fill the Marcus.

After Wednesday night let there be no doubt -- the Amp was as packed and rockin' as I've ever seen it.

The Black Keys – singer and guitarist Dan Auerbach and drummer Patrick Carney – has created a stunning oeuvre of gritty classic blues and R&B over the past decade and worked hard as a duo to bring those sweaty, dirty, roots-of-rock sounds to the stage Wednesday.

Across a 16-song set, plus a two-song encore, The Black Keys touched on all eras of its career, playing tracks from all its LPs except a tribute set and a disc of hip-hop collaborations.

But, unsurprisingly, the focus was on "Brothers," from which the duo highlighted "Everlasting Light," "Next Girl," "Tighten Up," "Howlin' For You," "She's Long Gone," "Ten Cent Pistol" and "Sinister Kid."

On a handful of songs, the pair was augmented by a keyboardist and bassist.

Despite the huge crowd and the Grammys and the chart success, The Black Keys still have an underground vibe that makes seeing the band at the Marcus an almost surreal, but entirely uplifting, experience.

If you feared there was no audience and no future for unadorned, down-home rock and roll, Wednesday's show should lay those worries to rest. The gig felt like a rock 'n' roll revival meeting.

The first opener, spunky, pop-punk outfit Cage the Elephant, hit the stage at 7:30 sharp with a howl of feedback and an explosion of sound marred by severely muddy low end.

But though the sun was still shining the Kentucky quintet played like it was onstage in a smoky rock and roll club and a good portion of those already in the then-half-filled bowl were on board.

Only two songs in, singer Matthew Shultz was already out in the crowd for the first of three visits sending security scurrying to prevent his mic cord from taking out the first few rows.

Despite the band's rocky relationship with Summerfest in the past it was on its best behavior Wednesday night.

Next up was Florence and the Machine, fronted by London's Florence Welch, which benefited from a much better sound mix.

The appearance of a harp onstage signaled that this band's set wouldn't likely have much in common with the raucous one from Cage the Elephant.

The performance focused, as expected, on material from the band's 2009 debut, "Lungs."

Welch, dressed in a long flowing dress, her hair blowing back thanks to a strategically placed fan, emoted over dramatic, sometimes atmospheric baroque, keyboard-laced rock, much to the delight of the by-then capacity crowd.