Last chance to leave a legacy?

Only a month ago, the common goal they sought seemed utterly unrealistic, a fantasy in the eyes of many. They were like Rapunzel's poor prince in Stephen Sondheim's "Into The Woods," trying to attain something that looked to be, well, unattainable. "Agony, beyond power of speech,'' the prince lamented. "When the one thing you want. Is the only thing out of your reach."

So many obstacles stood in the path of the 2009-10 Celtics as the playoffs began. To win, they'd likely have to beat the top two teams in the Eastern Conference without homecourt advantage. Check. To win, they'd have to regain their defensive focus and tenacity that was the hallmark of their championship team of two seasons ago. Check. To win, their top players would have to be healthy, or at least healthier than they had been in the regular season. Check.

And to win it all, they would have to do what they did two years ago, albeit without the homecourt advantage and against a more determined, humbled bunch of Los Angeles Lakers, who have very long memories. No check yet.

But the one thing the Celtics want is now well within their reach.

They enter the NBA Finals as almost the afterthought entry from the East, toppling favored Cleveland and Orlando in the process after a spectacularly humdrum season of 50 victories. They are the third-lowest seed (No. 4) to make it to the NBA Finals since the league went to a 16-team format in 1984. Should they somehow prevail, they would be the sixth-worst team to win an NBA title based on regular-season records in an 82-game season.

But dismiss them at your own peril. Certainly, the Cavaliers made that mistake after taking a 2-1 lead in the conference semifinals. And Lakers coach Phil Jackson is already mouthing off, trying to get the attention of someone. (The referees? His players?) You never know with Big Chief Triangle.

This Celtics team enters the NBA Finals with two driving motives to bring an 18th championship to Boston: the urge for this particular group to add a second title to its resume, something captain Paul Pierce feels will legitimize him and stamp him as one of the Celtics' all-time greats. (He already stands as probably the greatest pure scorer in franchise history.) And the other urge is that all signs point to a diaspora after the end of the season. It may not be the closing of the proverbial window, but it could well be the end of this group as we've come to know it, with potential changes covering both players and management.

It has been Pierce who has vocalized these twin sentiments time and again, although they pretty much rang hollow until deeds finally backed up the words.

"I think about [the window of opportunity],'' he said. "I think about all the great players from the past, to have played on the great Celtics team, [players who] have done it more than once. We want to be mentioned with the great players. After you do it [more than] once, you solidify your position in history as a great player. I'm trying to do that."

The great Celtics championship teams did, indeed, win in clusters. Or at least more than once. Longtime Celtics general manager Jan Volk, whose tenure with the team touched three decades and a handful of titles, thinks it's a tribute to the organization that the current players feel the need to add a second title.

"I think it's a tremendous commentary that that is the standard that applies,'' he said in a telephone interview. "They look around and see what happened in the past and I can see where they feel that it is a certain mark of achievement amongst themselves and within the organization.

"The players themselves feel that importance,'' he continued. "It shows they understand the tradition and that they have chosen to embrace it. As far as management and coaches, I don't think we ever looked at it quite that way. I know I didn't look at a player any differently if he had only one. But how many great Celtics have only won one?

That's what's bugging Pierce. The Bill Russell-led Celtics set the bar impossibly high by winning 11 times in 13 years, including an unfathomable eight in a row. The John Havlicek/Dave Cowens-led Celtics won twice (and should have won at least three.) Havlicek, who won eight overall, remembers his last two as being particularly special because they came without Russell.

"I kept thinking, 'I hope I can be on a couple teams [after Russell retired in 1969] that win it all,''' Havlicek said in a phone interview. "And when we did it, it was all that more fulfilling. One is never enough, although a lot of people shoot for one. If these guys get their second, it will be pretty gratifying."

The Larry Bird/Kevin McHale/Robert Parish-led Celtics won three and made it to five NBA Finals. McHale was asked in a conference call this week about Pierce's feelings that one title is simply insufficient using Boston's exalted championship mathematics.

"We never thought three was enough,'' he said. "Red [Auerbach] would always come in and tell us that we were supposed to win the championship that year and if we didn't, it wasn't a good year. But I think there's something to [what Paul said]. I'm glad to hear him say that; there are a lot of guys who would be content just winning one. I think he's got a good handle on it. Multiple championships are what set you apart and make you special. And he understands down the road that the Celtics are getting close to seeing their window close. There's a sense of urgency there."

There is indeed. When the new Big Three came to town, it was generally acknowledged that there would be a three-year window to seriously compete for a title. This is Year No. 3.

This summer brings the free agency of Ray Allen, who has shown throughout the season and the postseason that he still has game. He will turn 35 next month and has played 14 years and more than 40,000 minutes in the regular season and playoffs. But as one league executive put it, speaking on the condition of anonymity because of tampering rules, "I don't see Ray getting an offer out there that would be any more than what the Celtics could, or would, pay him. And he has said he wants to stay."

Allen appeared in 80 games this past season. He takes care of himself with Swiss efficiency and Prussian discipline. Once the trading deadline passed in February, and he was certain he'd be a Celtic for the rest of the season, his game took off. He averaged 20 points a game in February.

Allen has said repeatedly that he is comfortable in Boston and would like to remain there. And the unnamed executive is probably correct; it's hard to envision a scenario in which another team would shower Benjamins on 35-year-old Ray Allen.

Allen is really the only major player in this situation, although a handful of teammates will likely join him as free agents come July 1. They include Brian Scalabrine, Nate Robinson, Marquis Daniels and Tony Allen. Pierce could opt out of his contract, but it likely would be done to sign a new extension. He has said he wants to remain a Celtic for life and ownership is not concerned that he will opt out and go somewhere else.

A potentially larger issue concerns the coaching staff. Will Doc Rivers return for the final year of his contract? He has said only that he will do what he has always done since taking the Boston job in 2004 -- reflect on everything over the summer and make a decision. But it's hard to envision this group of Celtics being coached by anyone else. They are comfortable with him and he is comfortable with them. Plus, the Celtics gave him an extension after his first three, losing years, and there might be a feeling on Rivers' part to honor the deal, which pays him around $5.5 million a year.

Lately, the architect of the Celtics' smothering defense, assistant coach Tom Thibodeau, has become one of the hot names to fill any number of vacancies. He already has been offered the New Orleans job, according to an ESPN.com report. With so many openings (six right now, including potentially attractive ones in Chicago and Cleveland), he could well land his first NBA head-coaching job. Thibodeau has been a big part of the Celtics' success. What no one knows until he gets a chance is whether he will become a good NBA head coach or is destined to be simply a great assistant. And who would be the defensive guru on a new Celtics coaching staff?

Celtics watchers who followed this team throughout the 2009-10 season figured the postseason discussion as to the whereabouts of Ray Allen, Doc Rivers and others would already be well under way. They stumbled to a 27-27 finish over the final 54 games. They devolved into a negative rebounding team. Only seven teams turned the ball over more than they did. Kevin Garnett looked like he was playing with a ball and chain attached to his right knee. They looked, well, old and slow. They lost home games to New Jersey, Memphis, Washington and Philadelphia.

They looked a lot like the 1968-69 Celtics. That team also had a bunch of 30-somethings (Bill Russell, Sam Jones, Bailey Howell, Satch Sanders). It won 48 games and, like this team, finished in fourth place. It then awoke for the playoffs and dispatched of the Sixers in five games and the hated Knicks in six games before summoning up all that mattered to beat a star-studded and heavily favored Lakers team in seven games in the NBA Finals.

Few gave the 1968-69 Celtics a chance in the playoffs. Except the players. Just like today.

"Bill Russell took the last two weeks of the season off to rejuvenate himself. That's more or less what these guys did,'' Havlicek recalled. "Then, when the playoffs started, it was 'Let's get ready.' For us, we had beaten the teams during the season so we knew we could win. It was simply a matter of trying to force another one out of those old bodies. We had the experience and the know-how, and we used that to our advantage."

Russell and Sam Jones both retired after that season.

This Celtics team again faces a formidable Lakers opponent, but feels it has the experience and know-how of which Havlicek spoke to beat them. It has a starting five that, when intact, has never lost a playoff series. It has done what Rivers said it would do -- come together at the most important time -- and now has a chance to do what few thought possible when the playoffs began.

It will be a series that the current Celtics hope will put this group in the same discussion with other great Celtics championship teams by annexing another championship in what most feel could well be the Last Great Roundup for this group.

"So many people have won multiple championships, and you want to be in that group,'' Havlicek said. "Paul [Pierce] is absolutely right. And that's a good thing."

Added McHale, "We always looked up to the guys who came before us, Cowens, Russell. But you want to make your own history."

The opportunity is nigh.

Longtime Celtics reporter Peter May is a frequent contributor to ESPNBoston.com.