WALTHAM, Mass. – Paul Pierce has figured out how to help the Boston Celtics play better during the final minutes of their next playoff game against the Miami Heat.

He’s going to stick around.

Pierce was ejected from the series opener with 7 minutes left in the fourth quarter, and in Game 2 he strained his left Achilles’ tendon in the first half and was still hobbling down the stretch. He knows that Boston’s chances of avoiding a 3-0 hole depend on his ability to stick around at the end, and he plans to be there.

“Paul Pierce being in the game in the fourth quarter, healthy, is always going to help the Celtics,” he said before practice on Friday.

The Heat took the first two games of the best-of-seven Eastern Conference semifinals in Miami, and the series resumes with Game 3 tonight in Boston. For these Celtics, who have never fallen behind 0-2 since the New Big Three was assembled in the summer of 2007, it’s a crucial game to avoid what could be an insurmountable hole.

“We still feel like it’s going to be a seven-game series,” Pierce said. “I like our chances, especially with our backs against the wall.”

The Celtics have reason to be optimistic that they can at least make a series of it. They are back at home, where this core is 29-7 in the playoffs, and they expect to be healthier than they have been in a while, thanks in part to the three days off since their Game 2 loss.

That will help Ray Allen, who has a bruised chest from being elbowed by LeBron James, and Rajon Rondo, who has a stiff back. Pierce said his Achilles’ is fine, and Coach Doc Rivers said he expects to have Shaquille O’Neal coming off the bench for the first time in the postseason.

O’Neal has played just 5 minutes, 29 seconds since Feb. 1 because of a leg injury.

“Other than that, we don’t know what he can give us on the floor,” Rivers said, adding that O’Neal would not be limited in practice. “There’s no way we can get him at 100 percent. That ship has sailed. That would be a miracle. But we can get him to a point where he can help us.”

O’Neal came to Boston for just this time of year, but he missed the sweep of the New York Knicks in the first round and the first two games against Miami because of a calf injury in his right leg. The Celtics originally called it a “minor” injury, and he has been day-to-day from month-to-month, but he hasn’t gotten back on the court.

“We don’t know what to expect,” Heat guard Dwayne Wade said. “Shaq is a champion. He’s a guy who has won four rings. Having him back is going to be a boost in energy to the crowd and to the team. But it’s our job to go in and continue executing our game plan.”

Kevin Garnett says the Celtics are focused only on tonight.

“The whole thing’s a challenge,” Garnett said. “Our mentality is an all-in mentality for (tonight’s) game. … This is it. This is not a cool, kind of, ‘Keep your composure.’ No, this is ‘We’ve got to get the next game.’ It’s all-in.”