Teams trading All-Star point guards three months after meeting in the Eastern Conference finals is just crazy enough to make you believe the Earth really is flat, because the notion of two rivals ever agreeing on any deal where both sides could come out even is unfathomable. And yet it happened.

Only 81 minutes passed between The Vertical’s Shams Charania reporting the Cleveland Cavaliers and Boston Celtics were discussing a trade involving Kyrie Irving and Isaiah Thomas and Charania breaking the news that a deal was done. As a result, the two teams took a bulldozer to the rest of the East.

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In Irving, the Celtics finally land the superstar player they have long coveted with their wealth of assets. As president of basketball operations Danny Ainge said in a statement officially announcing the trade on Tuesday night, “Kyrie is one of the best scorers in the NBA. He has proven that on the biggest stage, the NBA Finals, the last three years. He’s been an NBA champion, an Olympic gold medalist and a four-time All-Star. For all he’s accomplished, we think his best years are ahead of him.”

True enough, under the guidance of LeBron James, Irving has transformed from an offensive wunderkind for a perennial lottery team to a bona fide legend with countless virtuoso playoff performances and one of the most clutch shots in NBA history on a resume that includes a ring.

There are real questions about whether Irving will revert to the player he was before James returned to Cleveland, but there’s no questioning his ability to raise his game when the lights are brightest. It is why he wanted out from behind LeBron’s shadow, and there are few bigger stages than a potential Eastern Conference finals rematch between the Celtics and Cavaliers, pitting Irving opposite James.

The Celtics revamped a roster that earned the East’s No. 1 seed in 2016-17, adding All-Star wing Gordon Hayward, No. 3 overall pick Jayson Tatum, forward Marcus Morris and center Aron Baynes, along with Irving, to a lineup that also includes All-Star big man Al Horford and recent lottery picks Marcus Smart and Jaylen Brown. Outside of Horford and Baynes, everyone on the Celtics is well under 30 years old, so young Boston coach Brad Stevens has a group to mold into a title contender for years to come.

That is, if Irving agrees to re-sign when it comes time to make a decision on his player option in 2019. Former Cavaliers general manager David Griffin suggested earlier this month Boston was among Irving’s preferred landing spots for all the aforementioned reasons, which leads one to believe a contract extension could come at any point in the next two years, but the Celtics have no guarantee.

And neither do the Cavaliers.

The Celtics gave up a king’s ransom for Irving: Thomas, a two-time All-Star who actually outproduced Irving offensively last season; ever-improving forward Jae Crowder; promising Croatian rookie 7-footer Ante Zizic; and the Brooklyn Nets’ unprotected 2018 first-round pick, which will almost certainly fall in the top 10 and could possibly turn into a No. 1 overall pick. It is enough to make rational folks believe Cleveland might actually break even on the point guard front and improve their depth on the flanks.

However, Thomas’ heroic 2016-17 campaign ended with a torn labrum in his right hip. That is no small concession, given the history of the injury, and as recently as early July his status for the start of 2017-18 remained in doubt. Late last month, the Celtics finally confirmed Thomas would not require surgery and was on target to begin the season. Even then, a report on the eve of Tuesday’s trade indicated Thomas was still scheduled for more testing at the start of training camp to confirm that diagnosis.

That, along with Thomas’ defensive limitations at 5-foot-9 (if that), led many in Boston to wonder if the two-time All-Star would be worth the max contract he will almost certainly demand next summer. Thomas and Ainge engaged in a playful back-and-forth about Thomas’ Brink’s truck sandals, made to symbolize the point guard’s repeated requests for a truckload of money in 2018 free agency.

Now, the Cavaliers face that same dilemma, when James will also be a free agent. There’s a real chance LeBron leaves as a free agent, and Thomas — after tasting playoff success and facing an uncertain future in Cleveland — could follow. The Cavs will have the insurance of a lottery pick, Zizic and Crowder’s bargain contract, which runs through 2020, but that’s hardly assurance of equal value for a player who is three years younger, six inches taller and considerably more accomplished than Thomas.

Both sides are assuming considerable risk, which makes this trade all the more fascinating.

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Thomas was beloved in Boston, inspiring a generation of pint-sized players sporting No. 4 jerseys. In two-plus years, he resurrected a franchise that had begun its rebuild in 2013, submitting an historic offensive campaign in 2016-17, all while playing for less than $7 million a season. He may very well make the Celtics regret this blockbuster deal, as could Crowder, whose toughness will also be missed.

Coupled with the loss of Avery Bradley — a salary cap casualty — Crowder’s departure leaves Boston without two key contributors on a defense that ranked fifth in points allowed per possession two years ago, and 12th last season. What the Celtics lost in physicality, though, they will hope to make up for in athleticism.

Irving, Hayward and Horford are all proven stars, and the rest of Boston’s roster consists of Swiss Army knives of positional versatility that arm Stevens with all sorts of matchup options. And if Marcus Smart and Jaylen Brown can fill some of the defensive void left by Bradley and Crowder, they’ll be all the better. Still, the Celtics will have roughly eight weeks to incorporate 11 new players into Stevens’ system before the season starts.

In Cleveland, that game-winning shot in Game 7 of the 2016 Finals cemented Irving’s legend. He emerged as an international icon, with his latest shoe ranking as the NBA market’s best seller. In recent years, he has made 40-point playoff performances seem routine, including a 42-point night to save Game 4 against the Celtics in June. Only nine players have scored 40-plus in an NBA Finals game over the past quarter-century. Their names are Michael Jordan, LeBron James, Shaquille O’Neal, Kobe Bryant, Charles Barkley, Allen Iverson, Dwyane Wade, Russell Westbrook … and Kyrie Irving. (Only Jordan, LeBron, Shaq, Wade and Kyrie have done it more than once.)

Still, while Thomas has yet to play on that stage, he did drop 53 points opposite Washington Wizards star John Wall while battling a bad hip, busted mouth and broken heart on his deceased sister’s birthday in the conference semifinals. It was the sort of effort that few NBA players could muster, much less a 5-foot-9 former last pick in the draft. Time and again, he has proven people wrong, and he will no doubt be looking to do so alongside All-Star teammates James and Kevin Love in Cleveland. With Crowder presumably joining free-agent signings Derrick Rose and Jeff Green on the second unit, the Cavs have also added athleticism to a bench that failed miserably against the Golden State Warriors with 30-plus-year-olds Kyle Korver, Richard Jefferson and Deron Williams playing major minutes.

The Celtics and Cavs were already heavy favorites to finish 1-2 in the East and meet in the conference finals again. While there’s a real chance both teams got stronger with Tuesday’s trade, the odds of each team winning the title remained the same, if only because the Warriors are almost unbeatable. It may take years to find out who won the deal — at least until Irving’s 2019 player option and we find out what becomes of Zizic and the Nets pick — but the focus in the East is, and will remain, on Cleveland and Boston.

Every other team in the conference will be an afterthought now that Irving and James — two former No. 1 picks who joined forces to bring the Cavs their only NBA championship — are on opposite sides of a rivalry that dates back a decade. Kyrie’s trade to the NBA’s most storied franchise breathes new life into the Boston-LeBron battles that began in Cleveland in May 2008, carried into the next decade in Miami, and fizzled to more of a hammer-and-nail relationship in recent playoff meetings.

Finally, finally, after seven straight years of penciling LeBron James into the Finals while the Western Conference battled it out for the right to face him, the Irving trade injected some intrigue in the East. And, wouldn’t you know it: They will meet in the first game of the season on national TV. It’s almost as if there was some grand conspiracy that led to them meeting like that. The NBA is a crazy flat world.

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Ben Rohrbach is a contributor for Ball Don’t Lie and Shutdown Corner on Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach

Related coverage from Yahoo Sports:
• Dan Wetzel: What the blockbuster trade means for LeBron
• How the Celtics granted Kyrie Irving’s wish
• Cleveland sets up for now, eyes future in Irving-Thomas swap
• LeBron’s Twitter farewell to Kyrie: ‘What a ride it was’