BOSTON – When Paul Pierce and Boston’s other starters need a rest in the NBA finals, they can watch their replacements with confidence.

Just as they did two years ago against the same opponent.

Two years ago, when the Celtics won their 17th title by beating the Los Angeles Lakers.

Boston’s substitutes have changed. The importance of their contributions hasn’t.

“Somewhere along the line these guys that are role players that people don’t really talk about come along and help us win games,” Pierce said. “They really get overlooked.”

The Celtics, who return to practice today after a two-day break, have the same starting playoff five for Thursday night’s opener at Los Angeles that they had the past two years, a source of comfort for Coach Doc Rivers.

That group has led them to playoff victories in five games over Miami and six each over Cleveland and Orlando this year. But through that run, substitutes Rasheed Wallace, Glen ‘Big Baby’ Davis, Tony Allen and Nate Robinson have had their moments — and more.

The latest and most surprising? Robinson’s 13 second-quarter points in Friday night’s 96-84 win over the Magic in Game 6 that sent the Celtics to the final round.

In Boston’s other 16 playoff games, Rivers didn’t use the 5-foot-9 leaper and long-range shooter in seven of them and played him for more than nine minutes just once even though he was healthy. In the 26 games Robinson played after being traded by New York on Feb. 18, he averaged only 14.7 minutes.

“I told him at some point it was going to happen for him and it was all up to him to stay engaged,” Rivers said. “And he did. I get no credit out of this.”

In 2008, it was James Posey, P.J. Brown, Leon Powe, Eddie House and Sam Cassell who watched the opening tips from the bench. But by the final buzzer, their performances — the numbers that show up in the box score and the defensive play that statistics don’t fully measure — were significant.

That year, Los Angeles’ second unit had played better than Boston’s in the three series each team played heading into their matchup. But the Celtics substitutes outrebounded those of the Lakers in all six games and outscored them in five.

In the opener, Cassell scored eight points and Brown had six rebounds in a 98-88 win. In Boston’s 108-102 Game 2 victory, Powe had 21 points. Then in Game 4, Posey scored 18 and House hit two 3-pointers that sparked a 21-3 run in the final five minutes that carried Boston to a 97-91 victory.

“If you look at our team over the last couple years, three years, we brought guys in the middle of the year to help us in these types of situations when we get to the playoffs,” Pierce said. “Last year we were injured. The year before it was P.J. Brown who came up big and won a game for us versus Cleveland, and this year it was Nate.”

Brown had 10 points and six rebounds in a 97-92 win in Game 7 against the Cavs that sent the Celtics to the 2008 Eastern Conference finals against Detroit.

But after that season, Brown retired, Posey left as a free agent for New Orleans and Cassell signed a one-year deal with the Celtics but never played with them again. Powe stayed another year, then joined Cleveland.

With Kevin Garnett out with a knee injury last year, Boston lost in the conference semifinals.

This year, the Celtics kept House until the trading deadline, when they sent him to the Knicks for Robinson, the latest backup to provide a playoff boost.

Allen played aggressive defense in the three series, Wallace averaged 9 points in the Orlando series after a poor regular season and Davis averaged 7.8 points and 4.8 rebounds against the Magic. A first-rate performance by the second unit.

“We call ourselves the ‘clenched fist,’ ” Davis said, “because when you clench your fist, you become strong. Together as one, you become strong.”