Taylor Swift attends the 55th Annual GRAMMY Awards at STAPLES Center on February 10, 2013 in Los Angeles, California. Credit: Christopher Polk/Getty Images

Taylor Swift's surprised face is so 2012. During the Grammy Awards at the Staples Center in L.A. on Sunday (Feb. 10), the 22-year-old singer-songwriter perfected a new expression: Number One fan singalong face! After opening the big show in a circus-themed (and Harry Styles-dissing) rendition of "We Are Never Ever Getting Back Together," the superstar stayed in the audience, but didn't exactly fade in the background.

An energetic admirer of many of the night's big performers, Swift was filmed throughout the night singing and dancing along -- she knew almost all the words! -- to The Lumineers, fun. and others.

By the single star's side for the spirited evening of fangirl-dom? It wasn't Swift's high-profile gal pals Selena Gomez or Dianna Agron, but, a source reveals to Us Weekly, Claire Waterman --  daughter of celeb jewelry designer Cathy Waterman.

Swift, who won a Grammy before the telecast for her Hunger Games track Safe and Sound, apparently didn't hit the big parties following the show.  "Video shoot early tomorrow, so my Grammy after-party situation looks like . . . " she wrote -- sharing a snapshot of her cat on Instagram.