Without much fuss, Belle And Sebastian and Yo La Tengo have eased their way into rock and roll middle age in the last decade. They're both clearly still beloved by fans who latched onto their quintessential, era-defining albums from the mid-to-late '90s, fans who see them to sing along with "Get Me Away From Here I'm Dying" and "Sugarcube" (but may or may not be as familiar with their recent—and still quite good—work). Despite a stylistic sonic gap between the groups, they proved to be completely complimentary entities on Thursday night when they co-headlined Celebrate Brooklyn at Prospect Park, and offered two ideas of how to age gracefully with guitars and horns.

Even at an outdoor event where they are ostensibly not the main act, Yo La Tengo shies away from anything too straight-forward—they do sprinkle in some of those spiky 3 minute long guitar pop nuggets like "Nothing To Hide" and "Tom Courtenay" into their sets, but those are mixed with the repetitive, krautrock-like grooves of "Stupid Things," "Before We Run," and "Ohm." They captured a moody, languid twilight sound, even though it was still light outside by the time they finished their set.

On stage, more than anything else, Yo La Tengo is defined by Ira Kaplan's ferocious guitar wrestling, which seems to be immune to aging. He swung his guitar like a golf club during "Ohm," and treated it like a squiggly dancing partner during closer "Blue Line Swinger." His tone still retains a Sonic Youthian heft, and he coaxes out a squall of noise just as easily as he did when he was in his 20s. At his best, Kaplan is the nebbishy guitarist equivalent of dancing Thom Yorke (just with less ponytail).

But while the crowd seemed to appreciate Kaplan's uninhibited moments, you could tell that the band lost them in those quieter, more drawn out ones—which is why at the end of the day, Yo La Tengo is a band made for playing intimate clubs like Maxwell's. Belle and Sebastian, on the other hand, have shed the skin of their insular Glasgow origins, and emerged as crowd-pleasers through and through. They also seem to have an inverted audience relationship with quiet: while people tended to chatter away during "I Don't Love Anyone" and "I'm A Cuckoo," they stood in stone silence and awe at the first lazy acoustic guitar strums of the brilliant "The Stars Of Track And Field" and "Lord Anthony."

There were only three or four songs that fit that vibe in the evening though—the bulk of their set was taken up by Belle and Sebastian Mark II, the group who have successfully embraced the sunny harmonies of The Mamas and The Papas, the arpeggiated chords of The Byrds, the winding guitars of Thin Lizzy, and the glam rock of T. Rex on their last three records (Dear Catastrophe Waitress, The Life Pursuit, Write About Love). These were love songs about faith ("Funny Little Frog"), love songs about football ("Another Sunny Day"), even a glorious disco-throwback ("Your Cover's Blown")—but they were always buoyant.

Belle and Sebastian don't have any new albums they're promoting (unless you count rarities compilation The Third Eye Centre), which made their set particularly telling: you can get a clear idea of who the band thinks they are right now by what moods and textures they chose to emphasize. And clearly, Belle and Sebastian Mark II is very comfortable in their new upbeat, outgoing guise—it seems like their fans have mostly embraced it as well, even if they still lose their collective minds over the shy bedroom chamber pop.

At least the two sides of Belle and Sebastian came together perfectly at the end of the set, when Stuart Murdoch invited all the attractive young people in the front row to dance on stage during "The Boy With The Arab Strap." It went so well, they let everyone stay and dance during another throwback—and one of the first songs that pointed in the direction they were going—"Legal Man."

Belle and Sebastian Setlist Prospect Park Bandshell, Brooklyn, NY, USA 2013