Way back in October when the Celtics gathered in Waltham for the start of yet another run through the long grind of an NBA season, their mission was clear. The ghosts of Game 7 in Los Angeles has haunted them long enough, and while they knew it would be eight months before they even got the chance to avenge that defeat, the goal of the regular season was two-fold: They needed to stay healthy and put themselves in the best possible position for an extended postseason run.

On the first count, the regular season has been more or less everything they could have hoped for. While the status of Shaquille O’Neal looms like a 300-pound elephant in the locker room, the big four of Rajon Rondo, Ray Allen, Paul Pierce and Kevin Garnett are as healthy as can be expected.

Pierce and Allen played 80 games and would have made it through the entire run if not for coach Doc Rivers sitting them out for the final two. Rondo battled foot and leg injuries in the early part of the season and a painful finger ailment late, but he seems ready to go physically. In perhaps the biggest surprise, and most encouraging sign, Garnett made it through the entire year except for a nine-game stretch with a calf injury and was able to recapture his form of a few seasons ago.

Shaq, however, remains a question mark. Rivers said before their final regular season game with the Knicks that Shaq’s availability for Game 1 was, “probably too early to tell, but I think so.” Team president Danny Ainge said Shaq was day to day and if Wednesday night’s game was in the playoffs instead of a meaningless showcase for the likes of Avery Bradley and Sasha Pavlovic, then Shaq still wouldn’t have been able to play. 

The Celtics can win their first round series with New York without Shaq, but beyond that is anyone’s guess. 

On the second matter, there is no doubt that the Celtics squandered a golden opportunity to make life less difficult for themselves this spring. They had the top seed in the Eastern Conference in their sights when the month of March began and the second seed all but assured as a fine consolation prize. They also had the advantage on the Lakers if the two teams were to meet once more in the finals.

Now all that is gone. Despite their 56 wins, the Celtics are right back in the same position they were a year ago with as many as three round of the playoffs ahead of them without the benefit of homecourt advantage.

If they fall short in a Game 7 on someone else’s court there will be bad memories of terrible defeats suffered at the hands of the Nets, Clippers and Wizards to name three. Not to mention the pair of close defeats at home to the Grizzlies and Bobcats in succession that knocked them out of the race for the top seed.

All that is in the past now and if anything the Celtics are relieved that the regular season is finally over.

“Now we can focus on just playing,” Rivers said. “Hopefully in some ways -- it’s not easier -- but easier to focus, clearly. I think this is what our guys should have been playing for all year. When you lose a Game 7 that sticks with you and it’s very difficult to get back through the regular season.

“The whole season you’re thinking about, ‘Gosh, we’ve got to go through 82 of these just to have a chance to get back to where we were at last year.’ Now, at least all that is gone. Now we can start trying to get back to it and finish the job.”

There were highlights to this season to be sure. Pierce, Garnett and Allen remained injury-free and thrived beyond most preseason predictions. Rondo had a two-month run as perhaps the best point guard on the planet before injuries, malaise and Derrick Rose shoved him out of the conversation. Glen Davis also had a breakout season, putting himself in the Sixth Man of the Year discussions for a time and moving himself from bit player to essentially the fifth starter.

The Celtics also managed to beat every good team in the East and scored impressive wins over the Spurs and Lakers. That was a far cry from last season when they continually came up short against the league’s elite during the regular season.

But what ultimately defined the Celtics season was the trading deadline deal that sent Kendrick Perkins to Oklahoma City and brought back Jeff Green and Nenad Krstic. Right or wrong, Perkins has served as a reference point for everything that has gone awry since, and if the Celtics fall short specifically because of a lack of size or toughness, the deal will have been a disaster.

Both Green and Krstic have had their moments since their arrival, but neither has staked out a consistent role with the team yet and their playoff performances will be heavily scrutinized.

As the Celtics head into the postseason, there are parallels to last season when a hot start gave way to a frustrating second half of the season. They are some striking similarities between the two, but also some noticeable differences. Last year’s team was consciously put into hibernation while Rivers allowed Garnett and Pierce time to rejuvenate their bodies. This team was never meant to follow that formula.

Rivers, in particular, doesn’t want to hear about how similar the two seasons played out. Their health was their greatest opponent last season during the regular season. This year it was their focus and the unrelenting schedule that did them in down the stretch.

“I feel good that our team will be ready. I feel really good about that,” Rivers said. “This has been far more difficult than last year in that regard because of the trades, the injuries, [playing] seven [games] out of 11 [days], that’s been extremely difficult. We lost our rhythm, had no practice to get it back. And then we had injuries.”

The true test for the Celtics will begin Sunday when they begin their playoff series against the Knicks. “We’ll be ready,” Rivers vowed.

The regular season is already a memory now. It was filled with tremendous highs and shocking upheaval. The most fragile team in the league made it through more or less unscathed, but it’s hard to look past the six weeks of subpar play and inconsistent performances and not take note of the opportunities lost.