Gregg Popovich spoke for about 15 minutes, sometimes unable to hide his emotions, all the while wearing a T-shirt that had Tim Duncan’s face printed on the front. When the last question was answered, the coach turned, put his hands in his pockets and silently walked into a new era for the San Antonio Spurs.It’s a day Popovich knew was coming.That clearly didn’t make it any easier.“He’s irreplaceable,” Popovich said.Choking up at times and making wisecracks at others, Popovich bade a public farewell to Duncan’s playing career on Tuesday. The five-time NBA champion announced his retirement on Monday in a statement released through the team, ending a 19-year career that was spent entirely in San Antonio.“I figured I better come out here and do this and somehow say goodbye to him,” Popovich said.