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Taylor Swift used to crushing it in packed stadiums ... but, it was Travis Kelce 's Chiefs which did the crushing Sunday -- dismantling the Raiders while she watched.

The singer-songwriter -- who's kept a low-profile at her future husband's games this season -- was spotted sitting in her private box at the stadium.

It appears she's sitting with her dad, Scott Swift , too ... and, they watched a flaying by the Chiefs -- with one memorable NSFW moment from Patrick Mahomes in the 31-0 victory.

As you know ... Taylor has attended several games for Travis this season -- including one where she snuck in behind a protective screen -- though she didn't make an official debut until last week when she was finally spotted.

While it seems Taylor stuck mostly to the box, at lea

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