Chauncey Billups and Rajon Rondo were teammates on Team USA this summer before Rondo, the Celtics point guard, was released during the exhibitions leading to the World Championships. Billups led Team USA to Europe and a gold medal. Starting tomorrow at TD Garden, Rondo will try to lead the Celtics past the Knicks. The point-guard battle between the mysteriously slumping Rondo and the veteran Billups may become the most significant matchup of the first-round series, plus a matchup of distinctly contrasting styles. "He was playing good and we were both starting in the backcourt," Billups recalled of Rondo's release. "They just made the decision they wanted to move forward without him."