DETROIT — The Celtics are one victory away from taking their first trip back to the NBA Finals since 1987, when lost to the Los Angels Lakers, 4-2.

They are one victory away from adding another chapter in the book of the NBA’s most storied franchise.

They are one victory away from reaching a goal that every NBA team sets at the beginning of the season, but that only two teams can actually achieve.

That win could come tonight in Detroit in Game Six. The Celtics lead the best-of-seven Eastern Conference Finals series by 3-2, and Boston has never lost a seven-game series in franchise history after leading 3-2.

“We’ve got to have a great focus and a great intensity there,” Boston coach Doc Rivers said. “You know, they’ve won titles, they’ve been in this position before. We just have to go in there and play our game. That’s the whole key. Whatever happens, happens. But we’ve got to make sure we play our game. We can’t get caught up in anything that they’re doing.”

The Celtics would like nothing more than to end the series tonight at the Palace of Auburn Hills instead of losing and having to play a do-or-die Game Seven at the TD Banknorth Garden, where Detroit has already won twice this season — once in the regular season and in Game Two.

“We want to win this now if we can,” Rivers said. “They’re not going to let us win it. We’re going to have to come in and take it. They’ve been in situations before. They’re a tough, mentally tough, team, and we’re going to have to play the game of our lives to go up there and win, but I think we’re capable of doing that.”

Boston was in this position in both the Eastern Conference quarterfinals and semifinals, but lost Game Six to both Atlanta and Cleveland.

“We have a chance to end it,” Rivers said. “But you know, we’re playing good teams, and good teams in their place, and they’re tough to play. We just have to come in and have great focus and play. We can’t worry about if we win or if we lose. We have to just focus on the game and just stay there.”

Boston was able to put itself into the driver’s seat by holding off a late Detroit rally in Game Five to win a thriller, 106-102.

“We don’t get this game, we put ourselves in position to have to win another road game,” Boston captain Paul Pierce said after Boston Game Five triumph. The Celtics are 1-7 on the road this postseason.

“We know how tough it is to win out there in Detroit,” Pierce added.

Boston All-Star forward Kevin Garnett said, “We knew the significance of this game (Game Five). You don’t win this game, you put basically yourself in a corner. I thought we had good focus, good energy to begin with. I thought the third quarter was big for us. We came out with a lot of energy…Now it’s up to us to go up there and try to get one.”

There were several keys to Boston’s Game Five victory, all of which they hope to carry over to Game Six.

All-Star guard Ray Allen found his shooting touch again. He knocked down 60 percent of his shots (9-for-15) and finished with 29 points.

“If he plays like that, it’s tough to beat us,” Pierce said.

After being limited to 16 points in Boston’s Game Four loss, Kevin Garnett exploded for 33 points and 7 rebounds in Game Five.

“KG had a monster game,” Detroit coach Flip Saunders said.

Kendrick Perkins played the best postseason game of his career, finishing with career bests in both points (18) and rebounds (16).

“My thing is I’m going to leave it out there on the court, for myself, for my teammates and for everybody,” Perkins said.

While Detroit’s Big Three, Chauncey Billups (26), Richard Hamilton (25 points), and Rasheed Wallace (18) all got their points, the Celtics were able to contain Detroit forward Antonio McDyess, limiting him to just four points after he torched the Celtics for 21 points in Game Four.

If the Celtics can shoot as well as they did in Game Five (50.7 percent), take care of the basketball, force turnovers, and ride the defense that got them to 66 wins in the regular season by limiting opponents to 90.3 points per game (second in the NBA behind Detroit), the Celtics should be flying home from Detroit victorious.

The Pistons, however, plan on going back to Boston for a Game Seven.

“We’re not going away,” Saunders said.

roblee@projo.com