Now they're matched up in a playoff series that could be a seven-game classic.
In 2008, their playoff series went to seven games. It was far from a classic, however. All four games Boston won in that series were routs.
That was also the first year Boston's "Big Three" played together. Four years later, Kevin Garnett, Paul Pierce and Ray Allen are reaching the end of their career.
In addition, both teams' rosters are now totally different and key injuries have plagued them.
Boston no longer has players like Kendrick Perkins, Glen Davis, Eddie House, James Posey and Tony Allen that helped them become the dominant 66-16 team they were.
Atlanta, on the other hand, has evolved from a 37-45 eighth seed that was lucky to make the playoffs into a constant contender.
In fact, 2008 was the first time the Hawks had achieved a playoff berth in nine years. Atlanta now possesses numerous veterans with playoff experience.
Ray Allen is hurt. So on paper it would seem they could easily handle Boston.
Yet Boston has gotten the best of them all season. Even when Allen, Paul Pierce, Rajon Rondo and Kevin Garnett did not play, the Celtics nearly defeated Atlanta, losing by only five.
The Hawks sorely miss the inside presence of Al Horford and Zaza Pachulia.
Nevertheless, they did play well without Horford (who has been out since January 11th) for a time. Then their season got stuck in between a steady pace and regression. Pachulia's foot injury a few weeks ago only made matters worst.
Both teams simply have something to prove in this series.
Boston is playing for what could be Allen, Pierce and Garnett's last NBA championship ring.
To stand a chance, they'll need Allen to get healthy, Rajon Rondo to control his temper and their bench to provide full-effort. Keyon Dooling will need to step up his game tonight with Rondo suspended.
Atlanta is attempting to reach the NBA Finals for the first time since 1961 (ironically, all four of their NBA Finals matchups have been against the Celtics). However, I am sure they would be happy just reaching the Eastern Conference Finals.
Jason Collins and Erick Dampier (if he plays) have extensive playoff experience. Both have been to the NBA Finals, so they are suitable replacements for Horford and Pachulia. The problem is they are not known scorers, and neither is rookie big-man Ivan Johnson.
Therefore, most of the Hawks success will be depend upon Josh Smith and Jeff Teague continuing to play at a high level, Joe Johnson getting his offense on track, three-point shooting (looking at you Kirk Hinrich) and everybody else playing their roles on a consistent basis.
They also have to start games strong and maintain composure throughout all four quarters like they did in Game 1.
It would be nice as well to see Tracy McGrady show glimpses of the All-Star player he once was.
Odds are Boston may end up in a 2-0 hole without Rondo in Game 2. The Hawks are good enough to finish them off quickly, but never count out a team like the Celtics.
This series ends in six or seven games without a doubt, and will probably go the distance.