Barry Manilow was cruelly forced to cancel his Broadway opening last night after suddenly coming down with a case of brutal bronchitis following an interview with The Post’s often feared theater columnist Michael Riedel. We’re told Manilow and Riedel had a lengthy and friendly chat yesterday before both headed for a sound check at the St. James Theater, where Manilow was mobbed by women of a certain age outside. But once onstage, Manilow’s voice suddenly gave out, and he was forced to cancel the performance which was to be attended by critics. His rep said in a statement, “With deep apologies, and due to a sudden and brutal case of bronchitis, tonight’s show will be postponed until Feb. 26. Mr. Manilow can be found on the Brooklyn Bridge, getting ready to jump.” A source close to Riedel denied his interview had precipitated the steep decline in Manilow’s health, insisting, “Riedel spreads gossip, not germs.” Meanwhile there were scenes of chaos on 44th Street as fans learned that the show would not go on. One witness said, “A riot has broken out. Traffic is stopped on the entire street. There were middle- aged ladies losing their minds and mounted police.”