Liza Minnelli was forced to stop mid-song the other night after she got “too emotional” performing a medley originally arranged for her mother, Judy Garland, in 1951. A witness in the Las Vegas’ MGM Grand audience — which included Barry Manilow, Renée Zellweger, Alan Cumming and Kathy Griffin — reports that Minnelli “composed herself and finished the showstopper to a standing ovation.” The performance, a recreation of her “Liza at the Palace” Broadway show, was being filmed for a PBS special.