It sounded a little like 1999 inside Madison Square Garden Monday night. 

The heavily favored opponent couldn’t hold a lead.

The home team refused to give in, even as it trailed big early in the third quarter.

Thunderous chants of “deee-fense, deee-fense” bounced off the walls. 

And now, after another come-from-behind win in a postseason full of them, the Knicks and their fans can start to dream big — dream of a run like the spring of 1999 that took this franchise all the way to the NBA Finals. 

For the third time in this series, the Knicks eliminated a big second-half Celtics lead, and this time they did it in front of their fans, rallying from 14 points down to take a commanding 3-1 series lead with this 121-113 Game 4 victory. 

Mikal Bridges and Jalen Brunson took turns sticking daggers in the defending champions, and the Knicks were dominant over the last quarter and a half, outscoring Boston by 22 points in the final 20:47. 

“It’s the way we responded that I’m the most proud of,” Brunson said. 

Chants of “Knicks in five” echoed throughout the joyous building in the final seconds, as Tom Thibodeau’s team moved to within one win of one of the biggest upsets in Knicks history.

They can advance to their first Eastern Conference final in 25 years with a win Wednesday night at TD Garden. 

“A win like this was huge,” Josh Hart said. “Down at halftime, getting a lead going into the fourth quarter and not looking back.” 

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Making matters worse for the Celtics, superstar wing Jayson Tatum was lost to a noncontact injury late in the fourth quarter.

Tatum was writhing in pain on the Garden floor, clutching his lower right leg, and was helped off the court.

He was later shown in the tunnel in a wheelchair. 

Coach Joe Mazzulla called it a lower-body injury and said Tatum will have an MRI exam on Tuesday.

But it appeared to be an Achilles tendon injury. 

“We’ll know [Tuesday] exactly what it is, but it’s tough to watch a guy like him get carried off,” Mazzulla said. 

Tied at 102-102 midway through the fourth quarter, the Knicks ripped off a 14-2 run to ice it. Brunson and Bridges, the two Villanova teammates, scored nine points in the burst. 

Brunson finished with 39 points and 12 assists, Bridges added 23 (10 in the fourth), seven rebounds and four steals, and Karl-Anthony Towns had 23 points and 11 rebounds.

OG Anunoby broke out of his recent scoring slump with 20 points and Mitchell Robinson (eight rebounds) was a force on the offensive glass. Tatum poured in 42 points and seven 3-pointers for the Celtics in defeat before his injury. 

“It takes a whole team to beat them,” Towns said. 

The Knicks played better in the first half compared to Game 3’s rout, but still trailed by 11 at the break, mostly due to the Celtics making 12-of-24 3-point attempts.

The lead was extended to 14 early in the third quarter. It was starting to feel like Saturday afternoon’s one-sided Celtics victory.

The Garden was quiet and the Knicks were struggling to defend Boston. 

Then, Brunson caught fire. Out of a timeout, he sank a 3-pointer, then scored on a drive. It was still a double-digit difference with 6:43 left in the period.

At that point, the Knicks really took off.

They reeled off 21 of the next 29 points, 11 coming from Brunson. 

“Honestly, do we all expect anything less?” Towns asked rhetorically. 

They had momentum and the lead going into the fourth quarter.

When Bridges scored on consecutive possessions to begin the final period, the Knicks were up five and the Garden was on fire.

The decibel level kept increasing.

Brunson, Bridges and Co. were headed to another stunning win over the Celtics, now one victory away from sending the champs home.

But nobody inside the home locker room was celebrating just yet. 

“The toughest game is the game to end someone’s season,” Towns said. “To close out the series, you have to execute at the highest level possible, and that’s what’s going to be needed if we expect ourselves to be moving to the next round.”