Sean Penn and Petra Nemcova attend the Elton John AIDS Foundation Oscar Party on February 24, 2008 in West Hollywood, California. Credit: Jon Kopaloff/FilmMagic

Take two!

After a weeks-long fling in February 2008, Sean Penn and Petra Nemcova are giving it another go.

On May 10, a witness saw the pair "holding hands" during U2 frontman Bono's star-filled 52nd birthday bash at NYC's the Spotted Pig. After Penn, 51, and the Czech model, 32, mingled with revelers -- including Gwyneth Paltrow and Jay-Z -- "they left together," adds a second onlooker. 

It's Penn's first high-profile hookup since Scarlett Johansson, 27, with whom he split after four months in June 2011.

And the Oscar winner's quite the rebound for Nemcova, who announced April 11 she had called off her engagement to British actor Jamie Belman, 26: Explains a source, "Petra started going on dates with Sean right after the split."