The Chainsmokers nearly brought down the house at an Ohio State frat ... and it looks like the college rager of the year.

It all went down at the SAE house ahead just before one of the biggest college football games of the season ... with OSU squaring off against the Texas Longhorns.

Check out the video ... the place is jam-packed with students crammed together, jumping up and down as they hype themselves up for the big game.

We're told the set was a massive surprise -- not just to partygoers, but even for the SAE frat bros, who had no idea the duo was showing up to perform. Gallery Launch Gallery Getty

Apparently, The Chainsmokers just rolled up to the party ... and since the frat already had a booth set up for other DJs, Alex Pall and Drew Taggart just hopped on and did

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