Both stars enter their second-round clash with plenty more to prove.
Most immediately, Irving and Antetokounmpo must show they can win a series against real playoff competition. The Boston Celtics and Bucks went a combined 8-0 in their first-round matchups, but neither the Indiana Pacers nor the Detroit Pistons were in fighting shape.
Blake Griffin wasn't healthy enough to make things interesting for the Pistons, who crawled into the playoffs, and Victor Oladipo didn't play at all for the Pacers, who were under .500 after the All-Star break.
A pair of sweeps without sweat.
Now the real work begins.
A Trial of Leadership
Technically, Boston's success against Indiana gave Irving his first playoff series win without LeBron James, but he hasn't proved he can lead a team to victory against a real postseason foe. The test ahead is important enough for that reason, but it'll also be vital to validate a dismissive approach to the regular season.
Notoriously woke yet exhausted by non-playoff action, Irving made it difficult for Boston to form good habits during the year. Why should any Celtic sweat the details if Irving wasn't going to? He also called out younger teammates (which drew a pointed response from Jaylen Brown). He was moody, he was disengaged, and yet he got credit for a chemistry-saving, device-free plane ride that seemed to unite the Celtics.
Charitably, you could argue Irving's devaluation of the regular season was evidence of maturity, of perspective. But it's hard to get past thinking Boston's malaise and disjointed play may have actually stemmed from that approach. Terry Rozier's comments, delivered to reporters after that pivotal cross-country flight in March, highlighted the impact a tonally inconsistent Irving had on the Celtics:
"Ky's our leader, and when he's in a great mood and he's feeling good, we're hard to beat and it's contagious. It rubs off on everybody else. Sometimes when he's not like that, it can get everybody uptight. So the way he's been acting has been great, and it's been good for us."
Great as he was statistically (Irving and James Harden were the only players to average at least 23 points and six assists per game on 59 percent true shooting), it's difficult to avoid attributing Boston's inconsistency and clunky chemistry to its best player.
If Irving plays well and Boston advances past a fearsome Bucks team, all of his mercurial missteps look more like pieces of a grand plan. Better still, success against Milwaukee could force a reconsideration of his history.
There'll be a counterargument against detractors who saw him as a stat-hoarder who couldn't win squat on those pre-LeBron Cavs teams. And those who pegged him as James' sidekick—free to enjoy the wins without getting blamed for the losses. Even those who thought his absence unlocked something special in last year's Celtics will have to recalibrate.
To change his narrative that extensively, Irving will have to go through Antetokounmpo, who has plenty at stake as well.
A Study in Contrast
Giannis led the Bucks to 60 wins and one of the 25 best average margins of victory the league has ever seen, but he'll need much more than a 4-0 walkover against the Pistons for legitimacy.
Milwaukee treated the regular season much differently than Boston did. It ran up ridiculous leads, blitzing opponents quickly enough through three quarters to render the fourth a formality. The Bucks played with urgency, treating November games like do-or-die ordeals in preparation for what they'd face in May and June. And while Antetokounmpo's transcendent season owed plenty to talent, his relentlessness was its defining feature.
He stewed for days over a December loss to the Pacers, prompting head coach Mike Budenholzer to tell ESPN's Kevin Arnovitz: "I think there is a variance in the degree of competitiveness [among NBA players], but he's off the charts."
You don't lead a team to top-four finishes in both offensive and defensive efficiency if the regular season doesn't capture your full attention. You don't bulldoze through defenses for a record 116 unassisted dunks if you're coasting.
The Bucks crushed everyone all year, but it was still fair to harbor doubts. Was Budenholzer's system a gimmick? Was it only a matter of time until it would be exposed in the postseason? Was Antetokounmpo's dominance partly fueled by an unusual, untested style?
If Antetokounmpo's Bucks bury Irving's Celtics, it'll be the best evidence yet that what we saw during the season was real.
The Bucks earned the top seed partly because Antetokounmpo played every game like it mattered. Boston may have finished fourth in the East because Irving didn't share that urgency. This series could determine whose strategy was sounder.
More than that, it could set major changes in motion for whichever team comes out on the losing end.
If Boston fails to advance past the second round, the likelihood of an overhaul increases. Irving could leave in free agency. If he re-signs, Anthony Davis might be inbound, which would necessarily mean Jayson Tatum, Jaylen Brown and others could be on the way out. Even Al Horford has a player option.
A loss to Milwaukee could hasten the Celtics' restructuring.
The Bucks aren't exempt from big-picture alterations. Brook Lopez, Malcolm Brogdon, Nikola Mirotic, George Hill and Khris Middleton could all be gone in free agency. And if Milwaukee falls short of expectations, you'd better believe talk of Antetokounmpo's departure will increase in volume.
Davis made his trade request from the New Orleans Pelicans with more than a year left on his deal, which means Giannis' clock will start ticking well before his 2021 free agency.
When the Celtics and Bucks meet, everything will be on the line. The reputations of a pair of superstars, a referendum on leadership and the future of two organizations hang in the balance.