Rihanna Greets Fans Ahead of Concert with Surprise Jay-Z Performance

Rihanna had no problem taking time to pose with fans and sign autographs before a New Jersey concert last night in which Jay-Z surprised the crowd and joined the singer onstage. 

Rihanna -- who emerged from her hotel Thursday with a pony tail and wearing a sexy black dress -- decided to delight the waiting crowd before heading to her concert at the IZOD Center in East Rutherford, NJ.

At one point during the concert, Jay-Z rose from some smoke onstage to the surprise of a full house to perform with Rihanna the smash hit "Run This Town."