Corporate sponsors and recording artists sometimes make strange bedfellows. Case in point: the Honey Nut Cheerios' Sister Soulfest featuring Patti LaBelle and Chaka Khan, which came to Constitution Hall on Friday.

Who knows what round bits of oats have to do with two of the most accomplished R&B singers working today? But fortunately by the end of the sharp, tightly paced show, you'd all but forgotten the cereal that ostensibly brought you the soul.

Khan opened the show wearing a sparkly black mini-dress and blasting through "Once You Get Started," the 1975 hit recorded with her former band Rufus. Over the past few years, Khan's live show has devolved into a somewhat predictable hits package. But on Friday night, she shook things up, digging deeper into her catalogue to sing such little-performed numbers as "Please Pardon Me," "Hollywood" and "Do You Love What You Feel."

As a performer, Khan is a quirky eccentric with her jittery dance moves, crazy low-cut outfits and flaming red hair. LaBelle acts more as mama, dispensing life lessons, appeals to "love thy neighbor" and yarns about the importance of God and family. Vocally, Khan is a skillful and subtle stylist who emits awe-inspiring notes with the effort of an aside, but LaBelle is an all-out belter, selling a song by sheer force of will.

With a dizzying force that would have taxed performers half her age, LaBelle, 55, ripped through her hour-and-a-half set performing extended versions of her standards "Over the Rainbow" and "You Are My Friend," as well as a surprising batch of covers. Her spotty recording career attests to difficulties choosing her own songs, but she sure has an ear for those by others. On Friday, she did a thrill-ride version of Lenny Kravitz's "Fly Away" that recalled the glam-rock soul of her former group LaBelle, and gently slowed the pace with a take on Faith Evans's "Never Gonna Let You Go."

Well known for her onstage antics, LaBelle kicked off her shoes as expected, did her de rigueur roll on the floor, and even threw a microphone stand across the stage. Forget Cheerios--high-energy LaBelle has obviously been eating her Wheaties.