The Celtics had played that night without any of their three All-Stars. Gordon Hayward, lured from the very Utah Jazz team Boston had just beaten, was lost for the season on opening night. Kyrie Irving and his balky knee had played his last game of the season a couple of weeks earlier. Al Horford was sidelined that night by a sprained ankle.
Despite rolling out a starting five with eight total seasons of NBA experience, the Celtics found a way to beat one of the league's hottest teams, all while playing their third game in four nights to close a four-game road trip.
"That [road trip] might have been the moment where everybody was like, 'OK, we lost Ky, we lost Gordon, we lost [rookie big man Daniel] Theis, we don't have [Marcus] Smart right now, but we still have enough talent on this roster to go out and make some noise," backup point guard Shane Larkin said.
"That might have been the moment where we all kind of looked at each other and said, 'This is what we have. We're going to go out there and fight. We can do this.'"
But, as has been the theme of the season, these Celtics found a way to keep winning. And that night was just one of many moments that proved to Boston's players that they wouldn't go quietly in the postseason.
The Celtics return home to the comforts of TD Garden on Wednesday night with much of the NBA world ready to write them off yet again. The Cleveland Cavaliers have rallied to tie the Eastern Conference finals at 2-2, turning this into a best-of-three showdown for the right to advance to the NBA Finals.
Most young teams would consider themselves fortunate to simply be here with an opportunity to end LeBron James' reign of East supremacy. Not these irrationally fearless Celtics. While they most certainly had moments of doubt during the 2017-18 campaign, it was the adversity they routinely overcame that made this team believe that -- in the words of Kevin Garnett after Boston's 2008 title -- anything is possible.
But what's wild to think is that Boston might not have gotten this far, nor would its future be quite so bright, if not for all that adversity the team encountered this season.
These Celtics have so routinely overcome obstacles that players struggle to pinpoint a single moment that gave them the confidence that something like this would be possible. But all those experiences together leave them optimistic about their chances to keep their season going.
"We've been experiencing resiliency and adversity all year," Brown said. "That's nothing new to us."
FROM THE MOMENT the Celtics drafted Jayson Tatum, he asserted himself as not your typical 19-year-old. But in the moments before Boston's season opener against the Cavaliers in October, teammates saw their first glimpse of rookie jitters.
"He was a wreck," Horford said. "I knew right away. Right before the game I tried to loosen him up. He probably doesn't remember but I said something like, 'Hey, let's have some fun out here!'
"But you could just see it in his face, it was just so tense."
Tatum readily admits now that the butterflies were having a mosh pit in his stomach, especially when he walked onto the floor for his first NBA start and spotted LeBron James walking toward him.
Then a little more than a minute into the game, James swatted one of Tatum's shot attempts. Welcome to the NBA, kid.
"You're playing against LeBron James, you're matched up with him in the first game of the year. A lot of expectations. He had every right to be nervous," Brown said. "But you know what? [Tatum] finished with a double-double."
"We all kind of looked at each other and said, 'This is what we have. We're going to go out there and fight. We can do this.'"Celtics PG Shane Larkin
Which is to say that Tatum's nerves didn't last long. And it's about the only time he has looked like a rookie this season.
"Once he shook them cobwebs, man, they were gone," point guard Terry Rozier said. "And they ain't coming back. He's playing like he's been in the league for a couple years now."
The Celtics carried seven rookies as part of their 17-man regular-season roster. And while plenty was expected of Tatum as the No. 3 overall pick, even he exceeded expectations. On Tuesday, Tatum was voted to the NBA's All-Rookie first team.
More surprising were the contributions that Boston's unheralded rookies provide. German import Theis emerged as a key backup big before tearing his meniscus in March. Second-round pick Semi Ojeleye provided stout defense in limited minutes, then briefly elevated to a starting role against the Milwaukee Bucks where he battled Giannis Antetokounmpo and helped the Celtics survive that first-round series.
Boston wasn't supposed to have to lean so hard on these guys, but they were instrumental in getting the Celtics here.
Case in point: After starting the season 0-2, the Celtics were reeling after falling behind early in Philadelphia in the third game of the season. Celtics coach Brad Stevens inserted Jabari Bird, a rookie on a two-way G League contract and the No. 56 pick in last year's draft. Bird provided a defensive spark that helped Boston win the game.
The Celtics ripped off 15 more consecutive wins, routinely rallying from double-digit deficits along the way. A team left uncertain of its future after Hayward's injury developed chemistry and, maybe more importantly, much-needed confidence. And that stretch proved to the players that their season was far from over, no matter what pundits said of their chances without Hayward.
It's why when trying to pinpoint Boston's success now, players such as Horford look back to that stretch at the start of the season.
"I just noticed that it didn't matter the situation, we could have been down whatever and our guys just stayed focused mentally, and then just went out there and just grinded and worked," Horford said. "Good or bad, guys were still trying to play the right way, do the right things. We were making mistakes along the way but they were not shying away from the moment."
Horford marvels now at how far Boston's youngest players have come. Players such as Rozier have emerged as household names while filling in for All-Stars like Irving. Brown and Tatum are two of the most promising young players in the league. Assistant coaches swear it's all due to those players' commitment to improve individually, all while buying into what Boston was trying to do as a team.
Still, it's the spunk of all of these younger guys that resonates most with Horford.
"That mindset to just come out, work and play basketball," Horford said. "It's really inspiring."
BEFORE THE START of the conference finals, Stevens suggested there's a "power in being naive." The suggestion is that, while some teams get overwhelmed in pressure-filled moments, these young Celtics seem unfazed by much of the adversity they encounter. Boston has an uncanny ability to simply move forward, no matter what hurdles it encounters.
Injuries, double-digit deficits, LeBron James. Nothing fazes these players.
But why exactly are these Celtics so fearless?
"Because of what we've been through. We ain't got nothing to lose," Rozier said. "We got a lot of young guys that are hungry, we got a great coaching staff that puts us in the right position, and we got good veterans like Al.
"We got the right pieces, man, no matter who we're missing."
Brown, however, quibbles with the notion that the Celtics are naive.
"I see what Brad is saying but I would disagree. I don't think naive is the right word," Brown said. "I think we definitely know what's going on and I think we know who we're playing against. I think we know what we're up against.
"I just think that we have a lot of guys who have a really great mindset. ... But I don't think naive is the right word."
With every big win this season, the Celtics have seemingly become just a bit more fearless. Getting throttled in Milwaukee in Round 1 was an eye-opening experience after jumping out to a 2-0 series lead, but Boston found a way to scrap its way to a win in seven games.
Boston was the far more composed team in Round 2 against the Sixers. And all those regular-season rallies put the Celtics in position to charge back from a 22-point deficit to steal Game 2 against Philadelphia. Then, even when things got wild in Game 3 during the Confetti Game in Philadelphia, the Celtics never got rattled.
Now they must prove they can do it again. With the Cavaliers steadying themselves with consecutive wins in Cleveland, there's a notion that James & Co. cannot be deterred. After Boston's Game 3 loss, Brown said the rest of the world is already counting out the Celtics.
He might not be wrong. But these Celtics are certainly not counting themselves out.
This is just the latest adversity in a season in which they just keep fighting their way through it.