ABC's Nightline has done it again -- beaten both The Tonight Show With Conan O'Brien and The Late Show with David Letterman in total viewers. Moreover, it appears to be widening the gap between them. Last week, it averaged 3.59 million viewers to Late Show' s 3.28 million and Tonight 's 2.93 million. It also drew closer to overtaking Tonight among adults 25-54. While Tonight continued to lead in that demo with 1.58 million viewers, Nightline grew to 1.45 million. Late Show placed third in the demo with 1.21 million.