Only on Radar: Swift Duets With Mayer, Slams Joe Jonas?

Taylor Swift went from super fan to singing partner on Friday night, when John Mayer joined the 19-year-old onstage for the Los Angeles stop of her Fearless Tour.

"Taylor said she had a special treat for the audience and introduced him as her 'friend, John Mayer'" one concertgoer tells RadarOnline.com.

At LA's Staples Center, the pair sang two tracks together--Swift's "White Horse" and Mayer's sexually charged  "Your Body Is A Wonderland."

While not much was said between them, we're told that during "Wonderland" the two "got very close face-to-face and bumped guitars a couple times."

While Swift may swoon over Mayer, she might have had a message for ex-boyfriend Joe Jonas.

"When she was introducing 'White Horse' she talked about how in fairy tales you could always tell the bad guys  because they wear black capes," the onlooker says, "but in real life sometimes they are 'the one's that make you laugh and have great hair.'"

This could be a swipe at the excellently coiffed Jonas, who has been said to have broken up with Swift via text message.

Then again, perhaps she was gently ribbing Mayer for his laundry list of ex-girlfriends?

Regardless, last night must have been a personal triumph for the country crooner. She told People magazine earlier this month that, when first meeting Mayer at New York's Met Gala, she found herself gushing.

"I just respect him so much, I was rattling off quotes that he said in his blog, and he was probably like thinking that I'm a stalker," Swift said.

(Photo: WENN)