"Is it all right if he stays up here for another song?" Taylor asked the audience after dueting on "Your Body Is A Wonderland" before the pair started strumming "White Horse." John played a scorching blues solo on the second track, earning cheers from the crowd, who sang along to every word with the two musicians.
"I can't believe the Lakers get to play in the same arena that Taylor Swift performed in!," an impressed John Tweeted after the show.
Taylor's tour continues with a sold-out show in Las Vegas on Saturday night.
Related Content from AccessHollywood.com:
VIEW THE PHOTOS: Pop Stars
PLAY IT NOW: Access Search Engine: Taylor Swift's Wild Concert Surprise (May 7, 2009)
PLAY IT NOW: Access Extended: Taylor Swift Visits Contest-Winning High School