BOSTON — Shortly after Monday night’s 101-85 victory against the Philadelphia 76ers at TD Garden that put his team one game from advancing in the Eastern Conference semifinals, Boston Celtics Coach Doc Rivers had to deal with the inevitable question – what now?

More specifically, how do the Celtics, who now lead this best-of-seven series 3-2, send this 76ers team with younger legs and unending resolve packing?

The 76ers looked cooked after losing Game 3 at home 107-91, and trailing by 18 in Game 4. But they came back to win that game 92-83 to even the series.

In Game 4, the Sixers outscored Boston 61-37 in the second half. On Monday, Boston beat the Sixers 101-85 after creating a 54-35 advantage in the final two quarters.

Back and forth it has gone, so Rivers understands that having the chance to put the Sixers away in tonight’s Game 6 will be a daunting task.

“It’s not going to be easy,” Rivers said when asked what the Celtics needed to do. “Listen, this series is hard.”

This isn’t just coach-speak. The Celtics at times have had trouble keeping pace.

“They’re a good team; they’re an athletic team,” Rivers said. “Every minute you think, like we’re leaking oil physically.”

The oil comes from some creaky but crafty players, specifically Kevin Garnett, Paul Pierce and Ray Allen, who among them have appeared in 356 playoff games.

Pierce insists a sprained knee he suffered in the first round against Atlanta isn’t an issue. He’s averaging more than 38 minutes a game against the Sixers but still, even when healthy, he isn’t the fleetest of foot.

Allen has been hampered by an ankle problem that has clearly affected his play.

As for Garnett, his only malady appears to be age. Yet in this series and the playoffs in general, he’s certainly not acting his age.

Garnett turned 36 on May 19, but he’s much older in NBA years, having joined the league right out of high school. This is his 17th season and his minutes are somewhat monitored, but Garnett and point guard Rajon Rondo have been the Sixers’ biggest headaches.

Both are averaging double-doubles against the Sixers. Rondo is averaging 14.4 points and 14.6 assists, Garnett 20 points and 10.6 rebounds.

Rivers admitted the team was looking to feed Garnett in the post in Game 5, and who can question that strategy.

Even though he missed some open shots in Game 5 he had been knocking down this series, Garnett still shot 8 of 17 in scoring 20 points.

The shooting statistic is significant since the Celtics are 1-3 in their two series when Garnett attempts 12 or fewer shots, and 6-1 when he takes 13 or more.

The Celtics feed off Garnett’s toughness and he fears neither the 76ers nor, apparently, their fans.

Garnett is sure to get an interesting greeting after responding this way to a question asking him to compare Philadelphia fans to Boston fans.

“Not even close, not even close,” Garnett said. “You’ve got fans and then you’ve got fair-weather fans. Take it how you want it.”

He wasn’t referring to Boston’s fandom as fair-weather.