Taylor Swift is on a roll. Today marks the halfway point of a four-show stint at Los Angeles' Staples Center, and she's already two for two on the celebrity guest appearances. On Tuesday night, Swift invited Justin Bieber to the stage to perform his smash single 'Baby' with her, and the next night, August 24, pop-rock singer Jason Mraz joined her to lay down his best-known hit, 'I'm Yours,' with her help.

Despite the fact that he was appearing in front of a sea of people, Mraz kept it casual in a plaid shirt, jeans, and a hat. He led Swift and the crowd through the catchy singalong tune, and by mid-song, the 21-year-old pop-country songstress took over and encouraged her fans to wave their arms with the chorus.

For the most part, Swift let Mraz do his thing, enjoying the view from the stool beside him and occasionally offering her voice to what quickly became a duet. Even though the audience came for Swift, they didn't seem to mind the Mraz blend that she introduced. "I couldn't love LA crowds more. I can't believe how awesome tonight was. And thank you @jason_mraz for singing "I'm Yours" with me!!" Swift tweeted following the concert.

During her set, the 'Sparks Fly' hitmaker delivered another cover, though without the help of the original artists, unfortunately. Swift offered her fans a rendition of the Beach Boys' 'God Only Knows' -- apparently a request from gossip blogger Perez Hilton. "@taylorswift13 P.S. Thanks for playing my request!!!! #GodOnlyKnows," Hilton tweeted last night.

Swift returns to the Staples Center on August 27 and 28, which gives her plenty of time to line up the next big duet. Who will it be?

Watch Taylor Swift Sing the Beach Boys' 'God Only Knows'

Watch Taylor Swift and Jason Mraz Perform 'I'm Yours'