The Dallas Mavericks needed late-game heroics from Josh Howard and Dirk Nowitzki to outlast the stubborn Memphis Grizzlies and remain unbeaten at home. Howard matched his season high with 27 points, six during a key fourth-quarter stretch, and Nowitzki added 21, including two free throws with 8 seconds left, in the Mavericks’ 108-105 victory over the Grizzlies on Saturday night.