Opportunity is a-knocking. The Atlanta Hawks need to usher it in. This could be a problem. At ushering, the Hawks aren't exactly world-class.

The Boston Celtics will be without starting guard Avery Bradley in tonight's Game 2 and presumably for the rest of Round 1. This calls to mind another Boston series in another Round 1. In 2012, the Hawks won Game 1 at home and had the chance to take a 2-0 series lead at Philips Arena against an opponent missing its best player -- guard Rajon Rondo, who'd gotten himself suspended.

The Hawks led by 11 in the second half. They lost 87-80. They lost the series in six games.

This isn't an exact parallel. Rondo returned (and was very good) in Game 3 and thereafter. Bradley doesn't figure to be back if this goes seven. Still, it should serve as a cautionary tale. So should last season's Round 2.

The Hawks dropped Game 1 to Washington, which lost its best player -- guard John Wall -- to a wrist injury. The Wizards were beaten in Game 2 here and should have been eliminated in five games. The Hawks went to D.C. and pulled one of their all-time playoff clunkers. They trailed by 21 inside the final eight minutes. They forced an improbable tie on Mike Muscala's 3-pointer. They lost on Paul Pierce's banker at the buzzer.

The rest of the series -- Wall returned in Game 5 -- was frantic. Everything kept coming down to Pierce shooting at the horn. (Or thereabouts. Al Horford trumped Pierce's late jumper with a forceful putback to steal Game 5.) The Hawks were much the better team but rarely looked it. By the time they got to the Eastern Conference finals, they were essentially spent.

A team lets a weakened opponent linger at its peril. The Hawks seemed slightly the stronger side entering the series, and now they have no excuse. They should win the series. If they get to 2-0, they'd stand a chance to close it out in five if not four. To let it go longer would make Round 1 more problematic than it needs to be and could have a carry-over impact on Round 2, where the Cavaliers would surely await.

The Celtics are again down a guard. The Hawks cannot let down their guard. Here endeth the lesson.

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