A lot of that confidence has to do with the apparent good health of Garnett, who, a month shy of his 37th birthday, remains the most indispensable and important player on the Celtics. He did not play in 12 of the last 17 regular-season games, including eight in a row, to rest an inflamed left ankle. He did not play in two losses to the Knicks last month.

It is impossible to overstate the importance of Garnett. Last season, during the playoffs, Boston was plus-138 in the 737 minutes he was on the floor. When he was not, the Celtics were minus-118.

It has been more of the same this season. The Celtics were plus-112 when Garnett played and minus-130 when he did not. And against the Knicks this season, according to NBA.com, the Celtics allowed 97.6 points per 100 possessions while Garnett was on the floor. They allowed 115.8 when he was not in the game.

Rivers has been careful when parceling out Garnett’s playing time, and he will probably do the same in the playoffs. That means Garnett will come out at the midway points of the first and third quarters, replaced by either Chris Wilcox or Shavlik Randolph, who has played well since signing with the Celtics last month.

Rivers also experimented with a taller starting lineup late in the season, featuring Jeff Green at small forward and Pierce at the big guard position. Green also figures to play a big role in this series, whether defending this season’s scoring champion, Carmelo Anthony, or trying to supply some offense of his own. His 43 points against the Miami Heat on March 18 were the most scored by a Celtic this season. It also was the most allowed by the Heat in any game this season until Anthony dropped 50 on them two weeks later.

The Knicks have history on their side. Since the 16-team playoff format was adopted for the 1983-84 season, the No. 2 seed has a 53-5 series record against the No. 7 seed. The last No. 7 seed to oust a No. 2 seed was in 2010, when the San Antonio Spurs beat the Dallas Mavericks. It has happened only once in the Eastern Conference, in 1998, when the Knicks upset the Heat in five games.

The Celtics have never been a No. 7 seed, though they have been a No. 8 on three occasions, the latest being in 2004. The team has not been in Boston since Tuesday, the day after the Boston Marathon bombings. They flew to Toronto later that day and then to New York on Thursday afternoon.

They practiced Friday at Columbia University.