Had Kevin Garnett made those three free throws instead of clanging the rim, and had Paul Pierce been one step farther from Kobe Bryant before the steal of the series, the Celtics would be getting a duck tour of Boston’s Championship Trail — Boylston Street to Tremont Street to City Hall Plaza — today instead of preparing for Game Six of the NBA Finals.

But Garnett did miss one with 3:54 remaining and the Celtics down by a point, and two with 2:31 to go and the Celtics down by two. And Pierce was within Bryant’s long reach from behind with 40 seconds to play and the Celtics down by two. Which is why the Lakers escaped the Staples Center with a 103-98 victory on Sunday night.

And that’s exactly what it was for Los Angeles. An escape. Boston could have won its 17th NBA championship Sunday night, even with another horrendous (43-24) start, but the Lakers, not the Celtics, made the plays in the last three minutes, sending the series back to the East Coast, where it will end tonight, or, worst case scenario, Thursday night.

Either way, it will end with a Celtabration. Why? Let us count the ways:

•The Celtics had to win a game out West and they did, with their record-smashing comeback from a 24-point deficit in Game Four. And, despite several concerns — injuries to Rajon Rondo and Kendrick Perkins, a health issue with one of Ray Allen’s children, Garnett in early foul trouble — they still almost ended it in Game Five.

•After a good night’s sleep in their own beds and some hearty New England fare instead of California cuisine, the Celtics, starting with Garnett, will start fast tonight. Count on it.

•Garnett has rebounded from subpar performances in these playoffs with chest-thumping zeal. He scored 16 points in a Game Four loss to the Pistons and came back with a superb 33-point effort in Game Five. Fifteen points in a Game Four loss at Cleveland and 26 points and 16 rebounds in a Game Five triumph.

Sunday night, Garnett scored only 13 points. He did grab 14 rebounds and make two steals, but he turned the ball over four times and said he played like garbage. He said he will do better tonight, and he will. Count on it.

•Pierce, who scored 38 points and passed for 8 assists, would have been the hero had the Celtics won Game Five. They didn’t, so he wasn’t. But with the hometown crowd filling his head with noisy encouragement, he will have a big game tonight. Count on it.

•Allen, magnificent of late, struggled on 4-for-13 shooting in Game Five. He will do better tonight. Count on it.

•Closer than ever to winning their first NBA championship, these veterans wanted to end it in Los Angeles when they had the chance. They failed. They will want to end it tonight to avoid a Game Seven. Yes, they have won two Game Sevens this spring, and yes, the Celtics franchise has never lost a Game Seven in the NBA Finals. But this team does not want to tempt fate against a club featuring the NBA MVP.

•The New Big Three has received help in the playoffs from various role players. Who will make a difference tonight? Kendrick Perkins was the standout in Game Five of the Detroit series (18 points, 16 rebounds) but has a strained shoulder, did not dress for Sunday night and may not be in uniform again tonight. Leon Powe had the night of his life in Game Two against the Lakers with 21 points but was scoreless in Game Five. James Posey buried four 3-pointers and finished with 18 points in Game Four of the Finals but scored only three points in 32 minutes in Game Five. He did have six rebounds.

An effective Rondo would make life easier for Boston, but if he is as shaky as he was in Game Five, Sam Cassell and Eddie House will get their shots. House scored 11 points when Rivers went to his shooting lineup in Game Four. Cassell scored nine in Game Five.

Without Perkins to clog the middle on defense, Doc Rivers will need veteran P.J. Brown to get in the way of Lamar Odom and Pau Gasol when they take it to the hoop. Posey will have to help, as well. Odom (8-10, 3-3, 20 points) and Gasol (6-10, 7-10, 19) had their best games Sunday night, a big reason the Lakers won. Derek Fisher made only 3 of his 10 shots but sank 8 of his 11 free throws for a solid 15-point effort, another contributing factor to L.A.’s success.

•Let’s remember that the Celtics have lost only one playoff game at home this spring, to the Pistons, and have played well in “must” games. Make no mistake, tonight is a must game. The Celtics will become the first NBA team to play 26 playoff games. They are banged up and tired. They have two chances to win one game, but the better chance is tonight. They will seize the opportunity. Count on it.

mszostak@projo.com