Jeffrey Osborne has long been one of the most appealing figures in black pop, but he has continually been overshadowed by other artists--Michael Jackson, Lionel Richie and the Pointer Sisters among them. As a result, he’s learned a thing or two about sharing the spotlight. Still, Osborne couldn’t have counted on being upstaged twice in his weekend shows at the Greek Theatre--by his opening act and by one of his backup singers.

Of course, Whitney Houston isn’t your run-of-the-mill opening act: She’s the hottest newcomer of the year and a promising addition to the lineage of top-flight, mass- appeal singers that includes Dionne Warwick (her cousin) and Diana Ross. Houston combines Warwick’s classy demeanor and cool attitude with a vocal style that ranges from the volcanic power of Chaka Khan to the angelic sweetness of the late Minnie Riperton. Just 22, Houston seems by turns little girl, classy lady and red-hot mama.

While Houston is a newcomer on the brink of stardom, Osborne is a veteran in a bit of a rut. He has lots of quality songs--the sensuous ballad “On the Wings of Love” and the sleek, sexy romp “Stay With Me Tonight"--but his presentation Saturday was a little pat. His patter was a bit slick, his song choices too predictable. It’s not that Osborne has lost his appeal; he just needs to shake up his act. Oh yes: The backup singer who stole the show was Joseph Williams, a runner-up to Sam Harris on TV’s “Star Search,” who proved to be a spot-on impressionist by singing all the male parts in “We Are the World.”