Pop music critic

As if he’d just been rustled from the pages of GQ, Robin Thicke breezed onto the stage wearing a sharp suit and a bright smile, neither the man nor his hair-care products acknowledging the rain gusting overhead.

“Can I take you to the mountaintop this evening?” the R&B singer asked.

Depends. How’s the weather up there?

Saturday’s Virgin Mobile FreeFest — the region’s largest annual pop music festival — was a soggy one, with an estimated crowd of 50,000 funneling through the gates of Merriweather Post Pavilion to hear 20 acts, including Thicke, Vampire Weekend, the Avett Brothers, MGMT and Icona Pop. For the fifth consecutive year, tickets were given away online for free. On site, plastic ponchos cost five bucks.

Still, nothing heightens the senses quite like a day in the rain. As fans’ clothing became sopped and filthy, vanity gave way to abandon. Phones were tucked away in dry pockets. Ears opened.

And they were treated to some of the biggest hits of the summer — a summer that would officially end at midnight.

Thicke delivered his contribution at the finale of a bubbly set, crooning his ubiquitous and hotly debated “Blurred Lines” as his wet shirt clung tight to his chest. Sexy stuff — enough to make screeching fans momentarily forget they were standing in a muddy field strewn with garbage.

Swedish duo Icona Pop enjoyed the festival’s first big shout-along earlier in the day with “I Love It,” a rowdy kiss-off anthem that still hasn’t lost its detonative charge after making huge waves in the States this summer and last. But the rest of the twosome’s performance felt like a caffeinated refusal to be exiled to one-hit-wonderland, their hollered hooks supported by smart synthesizer riffs.

There were plenty of other synthetic sounds to be heard near the festival’s Dance Forest stage, where various DJs, including Congorock and Manufactured Superstars, played numbing dance tracks that boasted weapons-grade bass. An earlier Dance Forest set from Atlanta’s Washed Out was far more agreeable, with plush electronic swells that seemed to shake free the first leaves of autumn like so much confetti.

Not quite as sensual but every bit as stylish was Sky Ferreira, the 21-year-old pop singer who was arrested on drug charges last weekend in New York and surprised FreeFest fans simply by showing up. Clad in a ratty Megadeth T-shirt and blue-mirrored sunglasses, she seemed more poised than aloof during “Everything’s Embarrassing,” her mid-tempo heart-squeezer about vulnerability and falling in love.

Scottish trio Chvrches were another refreshing surprise on the festival’s undercard, their icy, ’80s-inspired new-wave songs made warm by singer Lauren Mayberry’s thoughtful touch.

And while Americana stars the Avett Brothers often skew closer to the 1880s than Reagan-era top 40, the band spent their finest moments onstage injecting their emotive songbook with a welcome dose of classic-rock distortion.

But the day’s most sure-handed performance came from headliners Vampire Weekend, the indie-rock foursome that has spent three albums chronicling life in New York City to gobs of acclaim that now feel clearly deserved.

As the band juggled chirpy songs from across their young career, short-term nostalgics roared for the band’s earliest tunes, making new memories in the mud.

Lavanya Ramanathan contributed to this report.