Let's hope their first-round test against the Hawks has sharpened Celtics' mettle for rest of postseason

BOSTON -- The Celtics are off to the Eastern Conference Semifinals after a frustrating first-round series against the Hawks in the first round. As they did several times last postseason, the Celtics made things a lot harder on themselves than they had to.

But when it was time to step up and finish their first-round test, the Celtics passed with flying colors on Thursday evening. Maybe overcoming some adversity early this postseason will help them shed the unearned arrogance that occasionally creeps in and costs these Celtics games.

That was the case Tuesday when they could have earned a few extra days rest and more time to prepare for another battle with the Philadelphia 76ers. But the Celtics fooled around with the Hawks and blew a potential clinching Game 5 victory at TD Garden on Tuesday. That forced them to head back to Atlanta for another game against a desperate Hawks team, and they again fooled around for most of that battle.

But something clicked late in the game. The Celtics flipped a switch and became the team we all know that they can be -- and should be. Down by three with just over six minutes to play, the Celtics stopped messing around. 

After being outmuscled on the boards for much of the game, the C's started to push back on the glass. They started to body up on defense. And they started to generate great looks for each other rather than settle for hero shots. There was no running out the clock in this one; the Celtics decided to run the Hawks out of their own building instead.

The sum of all those things was an 11-0 run for Boston, leading to a 128-120 win and a ticket to the second round. In the closing minutes, the Celtics looked like the best team left in the playoffs. They looked like a team that could march to a title over the next few months.

The Celtics learned from their Game 5 loss and were not going to let the same things bite them in the rear Thursday night. When Marcus Smart was playing out of control, committing a bad turnover and jacking up a pair of ill-advised threes at the worst possible moments, Joe Mazzulla subbed him out and gave Smart a few moments to collect himself. He was on the bench for less than a minute of game action, but a much better Marcus checked back in.

Smart then fueled the final push to victory, driving and finding Al Horford for a massive corner three to give Boston a 116-113 lead with 3:35 to play. He hit a three of his own with 91 seconds left to put the C's on top 124-116, and sealed the deal with a driving layup 20 seconds later when the Hawks cut off an open passing lane to Horford in the corner.

Between Horford's three and Smart's buckets, Jayson Tatum hit his only two shots of the quarter: A stepback to put Boston up by six with 2:44 to play, and an emphatic putback on a Horford miss where he flew over a pair of Hawks defenders.

Tatum finished with 30 points, but he didn't force his offense in the closing frame. He played in the flow of the game, while also coming through with some big rebounds and a huge block. Jaylen Brown did the same, scoring just seven of his team-high 32 points in the fourth. Brown was a menace everywhere else to close the game, with his block on Dejounte Murray with 2:30 left eventually leading to Tatum's putback slam.

While the Celtics were getting the buckets they needed on offense, they made sure the Hawks couldn't do the same. After Trae Young scored 25 points in the first half, the Boston defense held him to just 1-for-13 in the second half. Young didn't score for the final 20 minutes of the game.

Everything that the Celtics let go wrong on Tuesday night, they made sure it all went right on Thursday. They sharpened their mettle as they closed off the Hawks, reminding themselves what they can be when they focus and play the way they need to play.

The hope is that the lessons learned from needing to play an extra game against the Hawks will carry over to what will be a grueling series against the 76ers. The Celtics have had Philly's number the last few years, but they can't rest on those laurels. They pretty much did that against the Hawks, and it nearly bit them in the butt. And the 76ers have much sharper teeth than Atlanta.

The Celtics were tested and learned lessons throughout last year's playoff run, but it looked like they needed a refresher course to start this postseason. It wasn't always pretty, but the Celtics got the job done. It was frustrating at times, but it has them battle-tested ahead of their next postseason war.