When TV on the Radio stormed through “Wolf Like Me” at the Virgin Mobile FreeFest on Saturday night, the New York rock band seemed to summon all the tension, restlessness and unflinching hope of a tumultuous post-9/11 decade.

An hour later, Deadmau5, the massively popular electro-house DJ famous for wearing an oversized mouse-eared helmet, was dishing up escapist electronic dance music that felt as thick and sugary as funnel cake. Fans bounced and bobbled, some sporting mouse helmets of their own.

Those two wildly disparate acts drew the most enthusiastic crowds at this year’s FreeFest, which brought 50,000 fans to Merriweather Post Pavilion on Saturday.

Over the course of 11 hours, they swarmed the venue’s grounds, pinballing between three different stages in hopes of catching performances from 20 acts, including blues-rock duo the Black Keys, hip-pop crooner Cee Lo Green and rock icon Patti Smith.

For the third year in a row, tickets were given away online for free — a tactic organizers adopted in 2009 in response to a recession that still refuses to let up. Backstage Saturday, Virgin’s founder Sir Richard Branson said he’d like to try and keep it that way. “I would love to see if we could do it indefinitely,” he said.

He also admitted that he’d rather be out watching Grace Potter and the Nocturnals, the Vermont group whose hard-charging roots-rock made Potter sound like the heir to Melissa Etheridge. Every ticketholder over the age of 30 seemed to be gathered under the Pavilion roof for Potter’s fiery performance, making her set the festival’s equivalent of adult swim.

The young’uns were camped out near a side stage dubbed the Dance Forest to see the likes of Porter Robinson, Calvin Harris and the Teddybears — a Swedish trio who wore large Deadmau5-ish bear masks. All three acts served up unrelenting, ear-splitting house beats while fans got their feet wet on a squishy dance floor made of mud.

A wiry set from New York punk-funk veterans !!! (it’s pronounced chk-chk-chk), felt like smart counter-programming to all of that overblown bass. “I heard this was the Virgin FreeFest,” frontman Nic Offer hollered. “Good! Because I hate virgins!”

As Offer strutted across the stage, his bandmates carved out their own piece of the spotlight with syrupy grooves and tightly-coiled rhythms. It was the signature sound of New York Cool nearly a decade ago and Saturday’s set was an argument in favor of a revival.

It was a FreeFest return for James Murphy, albeit a low-key one. Last year, he led his now-defunct band LCD Soundsystem through a euphoric headlining set on the Pavilion stage. This year, performing as a DJ in the Dance Forest, Murphy delivered an understated set of disco-house, pumping up the crowd with the declaration: “I hope it’s good.” It was, even if the tunes he played only tickled the pleasure centers that the LCD Soundsystem once colonized.

Between the Dance Forest and the West Stage, fans crowded various booths dedicated to a spectrum of charities: earthquake relief in Japan, at-risk youth, the homeless and building a skate park in Baltimore. There was also an information booth for homeowners facing foreclosure. Yowch.

Rapper Big Sean mentioned the recession once during his set on the West Stage, but the rest of his time behind the mike was spent self-aggrandizing and rapping poorly. Before performing his pillowy radio hit “My Last,” he offered some inspirational words: “Make sure you do the [expletive] you wanna do with this life” — proof that Lady Gaga’s believe-in-thyself affirmations have even spilled over into hip-hop.

Cee Lo Green let a little Pussy Cat Dolls spill over into his set when he crooned “Don’t Cha,” a song he penned for the Dolls in 2005. It earned a tepid sing-along that couldn’t compare to gleeful head-bobbing when he sang his foul-mouthed mega-hit “Forget You.”

Far less colorful sets came early in the day, including the boilerplate Brit-rock of Bombay Bicycle Club, the mishmash-ups of Eclectic Method and Alberta Cross, which offered a bland take on American Southern rock, bringing to mind Kings of Leon but without the stupidly catchy singles.

But it wasn’t the opening acts that stunk. The field where the West Stage stood was a soggy, muddy mess that organizers tried to make more tolerable by laying hay over. The smell brought to mind the festival’s original locale, Baltimore’s Pimlico Race Course, which hosted the festival for three years before organizers moved it to Merriweather Post Pavilion and decided to let everyone in for free.

Okkervil River had the first notable set of the afternoon, playing anthemic rock that felt like Arcade Fire without the inflated sense of self — even though Okkervil River are from Texas, where everything is supposed to be bigger. At one point, Will Sheff, the band’s bearded, bespectacled frontman, tried to get the audience to clap along to the music in sixteenth note pitter-pats, not realizing that these songs were tried-and-true fist-pumpers.

Australian synth-pop group Cut Copy also shined early in the day, attracting an oversized crowd to the muddy West Stage with a set that peaked with “Lights & Music,” a standout from the group’s 2008 album “In Ghost Colors.” A sea of fans swayed as one, with girlfriends seeking out a better view on their boyfriend’s shoulders. Once the first crowd surfer writhed near the front of the stage, it finally felt like a festival.

And it stayed that way until headliners the Black Keys finished things out on the Pavilion stage with their retro-fitted rock tunes. The Ohio duo seemed happy to carry the torch for the recently dissolved White Stripes with a slew of blues-rock tunes that were hard to fall in love with, but impossible to dislike.

But they sounded brittle coming after TV on the Radio, who somehow made room in their righteous, distorted swirl for the marvelous voices of singers Kyp Malone and Tunde Adebimpe.

The only set nearly as poised as TV on the Radio’s came earlier in the day from the inimitable Patti Smith. “Because the Night” may have been the most emotive song in her set, but her banter between songs got the biggest response.

She was greeted with a mixed cocktail of boos and applause when she referred to John Walker Lindh as “the Bush administration’s scapegoat.” She urged the crowd to think hard about the anniversary that was only a few hours away. “Remember who you were September 10th,” she said.

But who will we be on Sept. 12? And will we still be wearing those ridiculous mouse ears?