Jayson Tatum and Jaylen Brown are fulfilling their promise to each other

Ex-Boston Celtics center turned ESPN analyst Kendrick Perkins was the loudest among a growing number of people in and around the NBA calling for his former team to trade either Jayson Tatum or Jaylen Brown on Jan. 7, the day after they blew a 25-point lead to the New York Knicks and fell out of the playoff picture.

"They can't coexist," Perkins told a national television audience.

This came three weeks after an anonymous general manager told Bleacher Report's Jake Fischer of the developing All-Star wing tandem, "I think there's pretty widespread belief that they don’t work together."

Six months later, Tatum and Brown stand on the precipice of their first NBA Finals appearance, having scored or assisted 45 of the Celtics' 56 second-half points in Wednesday's come-from-behind road victory against the veteran Miami Heat in Game 5 of the Eastern Conference finals. Game 6 is Friday in Boston.

"We just got to come out and play basketball," Brown told reporters of his partnership with Tatum after Wednesday's 93-80 victory. "We feel like there's not a lot of people who can play basketball with us two. When he gets going, when I get going, we know that we're going to put ourselves in a good spot to win."

Brown is 25 years old. Friday's elimination opportunity will be the 24th conference finals game of his career. Tatum is 24 and has been alongside Brown for three of the Celtics' four East finals appearances since 2017. The thought of breaking them up now is as laughable to Boston's front office as it was then, only now the rest of the league has no choice but to acknowledge what Brad Stevens thought ludicrous back in January.

"They’re by far the least of my concerns," the Celtics executive told The Athletic's Jay King on Jan. 17.

Even these conference finals have not been void of criticism for the NBA's best 25-and-under duo. Their 13 combined turnovers in the Game 3 loss were met with doubts about their mental toughness against a Heat team that also bullied them in the 2020 conference finals. How quickly people forgot their efforts opposite Kevin Durant's Brooklyn Nets and Giannis Antetokounmpo's defending champion Milwaukee Bucks.

Tatum and Brown are not the players they were two years ago, and they are miles from blowing a 3-2 series lead to the Cleveland Cavaliers in the 2018 conference finals. They were respectively 19 and 20 years old at the time. Neither had made an All-Star team yet or even averaged 15 points per game, but there they were, Boston's two leading playoff scorers with a chance to eliminate LeBron James and reach the NBA Finals.

The bubble was an even better chance, but Miami's Jimmy Butler and Bam Adebayo manhandled them in six games. Boston finished last season .500, lost a lopsided first-round series to the Nets and looked every bit as mediocre to start this season. So, Tatum and Brown convened after that Jan. 6 loss to the Knicks.

“We see all the things about, 'We can’t play together,' and everyone in the media saying one of us gotta go,” Tatum told reporters a few days later. “We just had a talk about [how] we both want to be here and we both want to figure it out. There’s not many players in the league like JB. The grass ain’t always greener. ...

"I think the most important thing is we both want it extremely bad, and we want to try to figure it out together. For us to be on the same page is extremely important, knowing we've got each other's back and we're going to give it all we've got to figure this out, regardless of what people may say."

Since then, the Celtics have been the most dominant team in the league. Tatum made the All-NBA first team, and Brown is knocking on the door of a third-team selection. Together, they have pushed the Heat to the brink, and they will draw on their experiences against James, Durant and Antetokounmpo — the only others besides Miami to ever beat them in a playoff series — with their latest and best title shot on the line.

You might think Tatum and Brown are finished products, given how often we have seen them on this stage. Brown is one of eight players in NBA history to play more than 75 playoff games before turning 26, and only Kobe Bryant had more playoff points than Tautm's 1,508 at his age. (The late Los Angeles Lakers legend needed 10 more games and 124 more field-goal attempts to get there.) They are elevating into rarefied air.

Nobody is questioning whether the Celtics should part with one of them anymore. Instead, we are left to wonder how long they could play together, and what they might accomplish before they are done. Brown is signed through 2024, and Tatum can enter free agency in 2025, but they are convinced they can win a title this year, and that could be enough to convince them to tie their careers together in Boston for their primes.

First things first. One more win against Miami, and the three-time champion Golden State Warriors likely await in the Finals. Months after Jayson and Jaylen vowed to "figure it out," the NBA is theirs for the taking.

As Tatum tried to explain to everyone on JJ Redick's "Old Man and the Three" podcast back in February, "I couldn't imagine why you wouldn't want to have two of the best players that are under 25 on your team."

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Ben Rohrbach is a staff writer for Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach