Usher needs to watch his back — his heir apparent is here in the increasingly dynamic Chris Brown.Brown’s nearly sold-out concert at the Scottrade Center Thursday night was a tour-de-force of spectacular showmanship for the still-emerging young artist.And he didn’t even need the high-wattage star power of surprise guest Nelly, who came on at the end of the 90-minute set, to help make that happen.To accept all this, one must first give Brown a pass in the singing department. Brown’s voice is pleasing without being deeply soulful or showy, but he seemed to not call on it so much in concert. Most of the music was pre-recorded as well, with only a drummer and DJ on stage (the rules of what’s acceptable in concert long ago changed).Brown, otherwise a consummate live entertainer, had enough going for him elsewhere. In paratrooper-inspired gear, he was memorably lowered onto the stage like Tom Cruise in “Mission: Impossible” for “Wall to Wall,” the first single from his latest CD “Exclusive.”The frills, played out over a bi-level set, included lasers, pyro, costumes, and creative use of video projection, including an on-stage camera he played to that cast him in extreme close-up.