The Celtics were looking like contenders again, but Tuesday may have been their worst loss of the season

Jayson Tatum (left) and the Celtics were swarmed by the Wizards on Tuesday.Patrick Smith/Getty

WASHINGTON — After an uneven stretch following the All-Star break, the Celtics entered Tuesday night’s game against the Wizards once again resembling championship contenders.

Finally healthy, they’d won five of six games, including three blowouts in a row. There was good reason to believe the run would continue against a lottery-bound Wizards team missing two of its top scorers, in a road arena that was absolutely filled with green.

But as the night progressed the Wizards’ confidence and interest swelled and the Celtics looked like the team whose season will end in two weeks, rather than the one gearing up for a run that could last deep into June. The Wizards scored whenever they pleased, however they pleased, and ultimately rolled to a 130-111 win that is a new candidate for Boston’s worst loss of this season.

While this result will raise the blood pressure of Celtics fans who are becoming uneasy about this team’s ceiling, it certainly did not seem to bother the Celtics themselves. Players were smiling and loose in the locker room afterward. During interviews later, they mostly shrugged.

“It was just one of those nights,” coach Joe Mazzulla said. “Very rarely has that happened to our team, so just one of those off nights.”

“We just throw it away and get ready for the next one,” forward Jaylen Brown said.

Regardless, the Celtics may have made their playoff run more challenging. They are now 2 ½ games behind the first-place Bucks — three back in the loss column — with six remaining.

This setback removes some luster from Thursday’s showdown in Milwaukee. Now, the Celtics would need to win that game and have the Bucks lose twice more to even have a chance at the top seed.

But this reality did not really disturb the Celtics after Tuesday’s loss, either. Jayson Tatum quickly pointed out that, last season, Boston won road elimination games against the Bucks and Heat en route to the Finals. It’s doable.

“I don’t think nobody worries about where they place,” said guard Marcus Smart. “The playoffs are what matters. You’ve still got to go out there and play and win. So wherever we place, that’s where we’re at, and we’ll deal with it.”

Tatum had 28 points in a losing effort against the Wizards.Patrick Smith/Getty

This might all be true. Maybe seeding won’t matter. Maybe this was just one hiccup on a forgettable night.

But the setback was also surprising and seemingly unnecessary. The Wizards had lost eight of 10 games and appeared to be easing off the gas in search of extra lottery Ping-Pong balls. They were missing stars Bradley Beal and Kyle Kuzma, as well as starting center Daniel Gafford. And their fans were noticeably outnumbered by Boston’s.

But when the Celtics missed some clean 3-point looks at the start, the Wizards became increasingly emboldened as they rushed upcourt and found cracks in Boston’s transition defense.

When Washington was forced into half-court sets, 7-foot-3-inch center Kristaps Porzingis punished the Celtics with an array of off-balance, odd-angled jumpers. He shot 14 of 21 and had 32 points, 13 rebounds, and 6 assists.

“It was the best he’s played [against us],” Smart said. “He did exactly what he’s supposed to do. He’s 7-3, shot over the top of us. In a lot of these battles he missed those shots. Tonight, he didn’t.”

Tatum had 28 points and Brown added 18, but both watched the final nine minutes from the bench. Mazzulla pulled his starters with the Celtics trailing by 22 points, and second- and third-stringers actually provided a jolt, needing less than three minutes to slice the deficit to 12.

But the surge ended there. The Celtics were just 11 for 44 from the 3-point line.

“Playing from behind all night was tough,” Tatum said. “Obviously, we have to start better and we’ve got to learn from it. If we don’t, it’s going to be tough for us, and if we do, I think we’ll be fine.”

Tatum subbed out with 7:31 left in the first quarter, maybe his earliest rest this season, with Boston leading, 13-10. Washington went on a 13-2 run with Tatum on the bench.

On Sunday, Mazzulla said he thought it was actually good for the Celtics when they fell behind the lowly Spurs by 8 points early, because it ensured that his team would anticipate an easy win. The start of this game felt somewhat similar, but the bounce-back never came.

Forward Al Horford, who has been an elite 3-point shooter this year, was 1 for 7, with several bad misses. Center Robert Williams, who has been productive in limited action since returning from a hamstring strain, did not attempt a shot and grabbed just four rebounds.

Washington's Deni Avdija -- who finished with a team-high 25 points -- celebrates after a second-half dunk Tuesday night against Boston.Patrick Smith/Getty

Even when the Celtics trailed at halftime, 64-51, the deficit seemed manageable, especially considering the competition. But the Wizards were energized to start the third, and the Celtics played like they weren’t expecting it. They were consistently unable or unwilling to stop simple cuts and drives.

One of the worst came with 2:40 left in the third and the shot clock running down, when Kendrick Nunn slid to the hoop without a defender near him and threw down an uncontested dunk.

“Games like this are not supposed to happen,” Brown said. “You’re supposed to win. But it’s over with now. Nothing we can do about it.”