The Celtics are still prohibitive underdogs to win the 2013 NBA championship. They were an outside entity in the race even before they lost two regulars for the season to injury, and, plucky as they have been in recent weeks, their stock has fallen in the Las Vegas futures market. But it is an important sign for this team that those without the luxury of detachment are still taking them very seriously. The best team in basketball will never be caught overlooking a matchup with the Celtics. On Monday night, the locals were without Kevin Garnett, Rajon Rondo and Jared Sullinger, and still the Heat were fully engaged, their early stumble notwithstanding. Sure, there was a winning streak — now at 23 — on the line, and there was some talk in the Miami dressing room about avenging the January loss in Ray Allen’s return. But even those two factors don’t fully explain how raucously the Heat celebrated their two-point win before the media were allowed into their Garden digs. The Heat hooted and hollered and acted as if they’d defeated an important team. And, to the defending NBA champions, that’s what the Celtics represent. It doesn’t mean Miami fears the Shamrock or that the Celts would be given a snowball’s chance on South Beach of defeating the Heat in a seven-game series two months hence. But it’s fair to say the Celtics have Miami’s attention. And for a team that has been laying waste to the league this year, the respect of LeBron James and Dwyane Wade speaks a bit louder than that of the oddsmakers, no matter how well the numbers fit the latters’ argument. The C’s have won one of their three games against the Heat this season, and it could have been two of three had they made another play or two in the final minute or taken better care of the basketball all night. Twenty-one turnovers are a series of largely self-inflicted wounds against a team whose best offense is derived from transforming your largesse into points in the blink of an ESPN highlight.