MIAMI — The Boston Celtics offered a reminder Saturday night at Kaseya Center of why they finished the season with the NBA’s best record and entered this opening-round Eastern Conference playoff series against the Miami Heat as overwhelming favorites. While there won’t be a sweep after the Heat’s shocking Game 2 victory Wednesday night at TD Garden, there might yet be the expected four blowouts. Saturday, there was another one, with the Celtics pushing their lead to 29 on the way to a 104-84 decision to put them up 2-1 in this best-of-seven matchup.