They hated each other in the 1980s, when Ainge was a guard for the Celtics in the Finals against Riley's Los Angeles Lakers.
They hated each other in the 1990s, when Ainge was playing for the Phoenix Suns and Riley was coaching the New York Knicks and they both were involved in a brawl. Ainge and Riley ended up on the deck, Riley ripping his pants. It led to a record 21 players getting fined or suspended.
Since 2003, when Ainge was named Celtics president of basketball operations, they've hated each other as rival executives, with Riley in charge of the Heat since 1995.
"Danny Ainge needs to shut the f--- up and manage his own team. He was the biggest whiner going when he was playing and I know that because I coached against him."
Ainge's response: "I don't care about Pat Riley. He can say whatever he wants. I don't want to mess up his Armani suits and all that hair goop. It would be way too expensive for me."
The Celtics won in a 2010 playoff meeting. The Heat won in 2011. In 2012, the Heat won a seven-game classic in the conference finals.
Riley signed Ray Allen away from Ainge. Ainge beat Riley on signing Gordon Hayward.
Now a new chapter. There are new faces -- well, except for Haslem -- out on the court. There are new styles -- if there were a 21-player brawl today, there might be a congressional investigation -- being employed.
But this Eastern Conference finals series is still Heat-Celtics. And that means it's Riley-Ainge. These are their teams, with their character and carrying their legacy.
It has almost never let us down.
-- Brian Windhorst
Game 1, Sept. 15: Heat at Celtics | TBD on ESPN
Game 2, Sept. 17: Heat at Celtics | TBD on ESPN
Game 3, Sept. 19: Celtics at Heat | 8:30 p.m. ET on ESPN
Game 4, Sept. 21: Celtics at Heat | TBD on ESPN
Game 5, Sept. 23 (if necessary): Heat at Celtics | TBD on ESPN
Game 6, Sept. 25 (if necessary): Celtics at Heat | TBD on ESPN
Game 7, Sept. 27 (if necessary): Heat at Celtics | TBD on ESPN
How the Celtics got here
2019-20 record: 48-24 overall
Offensive rating: 112.8 (fourth) | Playoffs: 111.2 (seventh)
Defensive rating: 106.5 (fourth) | Playoffs: 102.7 (first)
Round 1: Def. Philadelphia 76ers 4-0
Round 2: Def. Toronto Raptors 4-3
The Celtics came into the Florida bubble with high expectations, and they have lived up to them. Boston has been terrific since arriving in Orlando -- largely because of the return to health by Kemba Walker. After the guard dealt with knee issues for the final two months of the season before it was suspended in March, and again when the team reconvened in Boston in June, Walker has been back to his usual self during the playoffs, flying around and making the kind of impressive change-of-direction moves that made him a star with Charlotte.
Boston also has managed to overcome the loss of Gordon Hayward, who suffered a Grade 3 ankle sprain in the team's first playoff game against the 76ers. The Celtics also escaped from a titanic seven-game struggle with the defending champion Raptors after largely outplaying them -- Boston lost heartbreakers in Games 3 and 6 -- to make it back to the Eastern Conference finals for a third time in four seasons. Now, Boston is four wins away from its first trip to the NBA Finals in a decade.
-- Tim Bontemps
How the Heat got here
2019-20 record: 44-29 overall
Offensive rating: 111.9 (seventh) | Playoffs: 112.9 (fifth)
Defensive rating: 109.3 (12th) | Playoffs: 105.4 (fourth)
Round 1: Def. Indiana Pacers 4-0
Round 2: Def. Milwaukee Bucks 4-1
The Heat have been the darlings of the bubble. They believed heading into the restart that their organizational culture gave them a huge lift in terms of being prepared for the mental challenges that came with being away from family and friends for so long -- and they were right.
The businesslike approach the Heat take as a team has shined brightly on the floor. After wiping out the Indiana Pacers in a first-round sweep, the Heat dominated the top-seeded Milwaukee Bucks in five games. It was one of the most impressive series by an underdog in recent memory, and Jimmy Butler led the way.
Throughout the playoffs, the Heat have received contributions up and down the roster, from veterans such as Goran Dragic and young difference-makers Bam Adebayo and Tyler Herro. The single most memorable moment so far probably came in Game 2, as Bucks star Giannis Antetokounmpo fouled Butler as time expired and Butler went to the line -- as players on both teams watched helplessly from the other side of the floor -- and made two free throws to win the game. The Heat outscoring the Bucks 40-13 -- Butler outscoring the Bucks 17-13 by himself -- in the fourth quarter to come back and win Game 3 is a close second.
-- Nick Friedell
Series key: How will Boston handle Miami living by the 3?
Here's a wild stat: The Celtics have ranked in the top six in opponent 3-point percentage every season for the past decade. And this series might come down to whether or not Boston's historically great 3-point defense can slow down Duncan Robinson and one of the best shooting outfits in the NBA.
During the regular season, Boston ranked second in the NBA, by allowing just 34% of its opponents 3s to find the bottom of the net, and the Celtics have been even stingier in the first two rounds this postseason, by holding the Toronto Raptors and the Philadelphia 76ers to a combined 29.2% from downtown.
But here's the thing, the Heat are not the Sixers. Miami is one of the best 3-point shooting teams in the NBA, ranking second in the league in 3-point percentage this season, and has been the most accurate 3-point shooting team in the East through the first two rounds of these playoffs.
Although Adebayo was runner-up the league's most improved player award voting this season, his teammate Robinson also exploded onto the scene, coming out of relative obscurity to log one of the finest catch-and-shoot seasons this league has ever seen.
Robinson made over 46% of 513 catch-and-shoot 3s this season. Here's the list of shooters in NBA history who have made more than 45% of at least 500 catch-and-shoot 3s in a single season: Duncan Robinson. That's it.
No Klay Thompson. No Ray Allen. No Stephen Curry. The only one close is Thompson, who has tried 500 catch-and-shoot triples in two seasons but never hit over 43.6% in either season. Robinson is a special talent.
Just like Thompson, Robinson can get hot and change games --- and series outcomes -- with his jumpers, but one reason Boston has put up terrific defensive 3-point numbers is because Jayson Tatum, Jaylen Brown and Marcus Smart are each proven edge defenders capable of closing out and contesting shots.
If the regular season is a fair indication, Boston should be confident here -- Miami has made just 32% of its 3s in the three matchups involving the teams heading into this series.
-- Kirk Goldsberry
Series key: How fouls could decide the East finals
I'd keep a close eye on how many trips the Heat make to the free throw line in this series. In terms of the four factors of basketball success, the Celtics' biggest defensive weakness during the regular season was their tendency to foul. They ranked 24th in terms of opponent free throw attempts per field goal attempt.
Meanwhile, led by Butler, Miami attempted the most free throws per field goal attempt (.299) of any team in the NBA. That has carried over in the playoffs, where the Heat's free throw attempt rate has jumped to .351 per field goal attempt despite the fact that their first two opponents (Indiana and Milwaukee) both ranked in the top 10 in lowest opponent free throw rates during the regular season.
In Butler and Dragic, Miami has two skilled practitioners of the dark art of drawing and selling contact. Much like when defending James Harden, opponents must remain disciplined and avoid reaching in, no matter how tempting it might seem. The Bucks failed that test too often in the first three games of their series, when they sent the Heat to the free throw line an average of 31 times per game. By the time Milwaukee learned its lesson, it was too late to come back.
Boston did survive giving up 31 free throw attempts in the January meeting between these two teams in Miami, but their matchup on the ESPN World Wide of Sports Complex during the seeding games was less encouraging. Even with Butler sitting out, the Heat got to the free throw line 39 times -- including 18 for Adebayo -- in a 112-106 win over a healthy Celtics squad.
Depending when Hayward is able to return, Boston fouls could have extra impact. Not only do those fouls send Miami to the line for efficient production, the Celtics also risk foul trouble that will force Brad Stevens to go deeper into his bench than he wants. Smart fouled out in only 16 minutes when these teams most recently met, and Tatum picked up his fifth foul in the third quarter.
-- Kevin Pelton