Before the Knicks (22-10) got off to their 18-5 start this season, before their late-season surge into the playoffs last year, and even before Mike Woodson was promoted to interim head coach last March, New York became a good defensive basketball team.

In fact, it was Woodson’s hiring as an assistant to former Knicks coach Mike D’Antoni prior to the 2011-2012 season that marked the end of a decade of poor defense in New York.

“When I came in last year I was brought here for the defensive part of it,” Woodson said before Thursday’s 100-83 win over the visiting San Antonio Spurs.

New York ranked 10^th in the NBA in defense when D’Antoni decided to vacate the head coaching position, and the team only got better from there, ultimately finishing fifth in defensive efficiency and holding opponents to a league-low 32.1 points in the paint per game.

But until recently, nobody noticed that the Knicks’ defensive intensity had dwindled. New York was at a torrid pace from 3-point range (the team averages 11.3 3-pointers per game, which leads the league) and Carmelo Anthony was playing like an MVP candidate, so nobody complained when they allowed an average of 100.3 ppg over their first nine contests in December.

Tuesday’s 100-95 loss to the Portland Trail Blazers changed that for a number of reasons.

First, it was the second time in as many games that the Knicks fell to an inferior club (they were coming off a loss to the Sacramento Kings). Second, the loss was due in large part to another slow start. And third, the Knicks yielded 21 points to rookie Damian Lillard, who is the latest point guard to burn the Knicks on the perimeter (opposing point guards have scored 20.5 ppg against New York this year — 23^rd in the NBA).

Woodson met the problem head on leading up to Thursday’s win. His first step was to show a video of the team’s early season performances, back when the Knicks were playing offense AND defense throughout the game.

“I thought that [perimeter defense] was slacking in really the last 10 games or so,” Woodson said after Thursday’s win. “Our defense kind of went the other way. We put a nice feel-good tape together this morning to show our players, based on how we started the season defensively — when we were No. 1 in defense and No. 1 in offense — so we were doing everything right at the beginning of the season and there was some major slippage. As a coach, I got to take some heat for that. Again, it’s my job to get guys to step on that floor and give 100 percent and play defense at a high level to help us win.”

As Woodson explained during Thursday’s shootaround, “Eight of the 10 games” the Knicks lost involved “bad starts in the first quarter.” However, that wasn’t the case on Thursday, and that has a lot to do with Woodson’s decision to move Marcus Camby into the starting lineup alongside reigning NBA Defensive Player of the Year, Tyson Chandler.

The Knicks had been playing small all season, with Anthony at power forward [Amar’e Stoudemire just returned from a knee injury but has spent his first two games coming off the bench], but Camby’s length caused havoc on pick and rolls.

New York is without starting point guard Raymond Felton (fractured pinky), so they’ve been forced to defend point guards with the aging Jason Kidd and Pablo Prigioni [this will change when Iman Shumpert returns from ACL surgery in the next few weeks]. However Camby’s presence allowed the Knicks to switch more on defense, which in turn helped to limit Spurs point guard Tony Parker to just 11 points and six assists.

“They switched a lot defensively, altered a lot of shots” Tim Duncan said after watching his team shoot 36.4 percent from the field. “Obviously Tony didn’t get off clean shots as he usually does. I didn’t get clean looks as well. Like I said, they defended well. Their size is a big part of that.”

Unfortunately for New York, keeping Camby in the starting lineup may not be a long-term solution. In addition to his own age and injuries (he’s dealt with calf problems this year), Camby struggles to defend the smaller, quicker power forwards that suddenly populate the league.

So while matching up Camby against Duncan and 7-0 Tiago Splitter makes sense, he’d struggle to defend players such as the Nets’ Gerald Wallace or the 76ers’ Thaddeus Young.

“I think it will be difficult, you know, when you have a smaller four out there,” Camby said. “We have to chase around those little guys. But we’ve been playing small all year, also. So, we have Melo at the four a lot and I think with Melo at the four and Tyson at the five, that’s pretty much been our best lineup.”

The Knicks will have a lot of “best” lineups this season.

As Stoudemire returns to form, he’ll either move back into the starting lineup or log significant minutes off the bench. Shumpert’s return will allow Kidd to defend shooting guards (he’s not fast enough to keep up with point guards anymore) and eventually Rasheed Wallace’s “stress reaction” to his left foot will improve to the point where he can return to the floor (the Knicks have looked better defensively this season with Wallace than without him).

Yes, the Knicks are dealing with several significant injuries, but Thursday’s win reminded everyone that they’re capable of elite defense. And when you have the league’s third most efficient offense, a little bit of D can go a long way.

“If you can play that way against the San Antonio Spurs, you can play that way against anybody,” Chandler said.