Jimmy Butler and the Heat give the Celtics exactly what they need: a challenge

Jimmy Butler gave the Heat the edge they needed to beat Grant Williams and the Celtics.Barry Chin/Globe Staff

The Celtics realized the Miami Heat considered this an important game when Jimmy Butler flew into Boston on Thursday after missing seven games with knee issues. Butler could have easily taken a few days off and joined the Heat on Monday in Memphis, but there he was announcing on Instagram that he was headed for Boston.

And Butler delivered in his return. The Heat, nearly healthy, pushed the Celtics to the brink, and then Butler sank two critical jumpers in overtime to give Miami the 120-116 win.

The Celtics were not good Friday. They were below average. They committed 20 turnovers. Jayson Tatum followed up his 49-point effort with 14 points and never got on track. The Celtics missed 30 3-pointers and seven free throws.

There’s a lesson in defeat, however. The Celtics have their share of weaknesses and Miami exposed those over this two-game series at TD Garden. Both games were playoff-type intensity, Wednesday because of the presence of the Prince and Princess of Wales and Friday because of the presence of Butler.

He gives the Heat an intangible that few players in the NBA have. The Heat are a tougher and grittier team with him on the floor. And they were determined to send the Celtics a message that championships aren’t won in December.

“Jimmy made two tough, tough baskets and that’s just credit to his skill and his work and his development,” Jaylen Brown said. “He gets going in games like this, on the road, hostile environment against a good team. Jimmy always looking to try to put the icing on the cake. Jimmy, a big-time player, made both (shots) in overtime that sent us home.”

Miami has had a plethora of injury and chemistry issues this season and Friday’s victory improved its record to just 11-12. But coach Erik Spoelstra knows how to play the Celtics, and they were going to ensure Tatum didn’t follow his momentous game with a parallel performance.

The Celtics needed a challenge. They needed to be pushed to learn exactly how far they are from the team they want to be in April. And the honest answer is they are still far away.

Not much came easy against the Heat, but Jayson Tatum did shake loose for a dunk as part of his 14 points.Barry Chin/Globe Staff

That does show how good the Celtics can be. Three of their five losses have come in overtime. Tatum had an open 3-pointer that would have put the Celtics up by a point late in the OT and he missed. It was one of those nights, but the Heat did something to cause those problems. It was not misfortune.

“When we’re playing as well as we’re playing, everybody’s going to be out to get you,” Marcus Smart said. “They going to do every little trick they can to get a win. That’s the responsibility that comes with it. That’s a compliment to us and for that we have to come out and be ready and we weren’t as ready as we usually are and they got the best of us.”

But it will benefit the Celtics in the long run. And Miami’s resiliency Friday is just part of the NBA. The Milwaukee Bucks lost at home to the Los Angeles Lakers. The Phoenix Suns dropped a home game to the lowly Houston Rockets.

Humility is part of the growth. The Celtics knew this would be a difficult game. It’s hard to beat teams consecutive times, especially archrivals. The Celtics will have to learn how to win when the 3-point shot is not going down, and they’ll have to take better care of the ball as they seek to make the extra pass.

These are things that can be corrected, but it makes coach Joe Mazzulla’s job perhaps easier when he’s trying to stress the importance of sticking to offensive concepts when pointing to a loss instead of a win. The Celtics weren’t exactly feeling themselves but they know they are an elite team.

It took months for the Celtics to reach that status last season. It took weeks this season.

“It shows how special of a group this is because for a team that’s just as competitive and has that talent on the other side, to (allow) that many shots and (commits) that many turnovers and lose by 4 points in overtime, it’s really encouraging,” Grant Williams said. “Our offense beat us tonight and our offense has saved us in a lot of games this season. We knew it was going to be a playoff environment. You’re not going to be perfect. You’re going to have to go into the drawing board and regroup and understand where we can improve. If you don’t have games like this, you won’t have the opportunity.”

The question is how the Celtics will respond to this loss Sunday in Brooklyn and Monday in Toronto and on a critical six-game road trip that takes them West and to an NBA Finals rematch with the Golden State Warriors.

Their casualness with the ball and sometimes infatuation with the 3-pointer cost them Friday, but they also learned they are beatable and vulnerable when they make those silly mistakes that plagued them last year. The good news is they have worked feverishly to reduce those mistakes overall. So this could be considered an aberration.