Defense ruled the day, but it was Boston's offense that sealed the game down the stretch.

In last night’s nail-biter against Chicago, points were predictably at a premium between two very talented, very defense-oriented teams. So when the Celtics were able to produce field goals on three consecutive possessions late in the fourth quarter, giving themselves a lead they would never relinquish, it was evident that they found some crack in the Bull’s system.

The first crack in the system is that when Jason Terry jacks up a wild, end-of-the-shotclock heave and it goes in, even Chicago’s defense can’t do much about it. But on the two possessions immediately following Terry’s 3-pointer, Boston converted by running the exact same set and simply using a different shooter. Let’s take a closer look at the set.

One of the most important aspects of Chicago’s defense is the way they switch repeatedly, constantly and aggressively. Screens are made less effective against Chicago because instead of trying to fight through, they trust each other defensively. And because the help rotations are normally so good, this can make for a very difficult defense set to break.

But one way to break it is to run a pick and roll with a versatile, talented big man and a versatile, talented wing. And that’s exactly what Doc drew up for Kevin Garnett and Paul Pierce on consecutive possessions. Here’s the first one.

The first thing to notice is that as soon as Pierce gets the ball with his back to the basket, the Celtics have overloaded the weak side of the floor. Nobody else is really involved in the set. It’s time for the old guys to go to work.

The second thing to notice is that Garnett feigns a lesser role in the play before hustling over to set a screen for Pierce. The goal of the play is to get Jimmy Butler, who is guarding Pierce, to switch onto KG, which is convenient for Boston because that’s Chicago’s goal too. Butler is stuck on KG, but he does a pretty decent job of bodying KG out of great post position. However, Joakim Noah comes down to help on Garnett.

Now Nate Robinson has to run over and ensure that Pierce doesn’t have an open three, but Pierce sees Robinson coming and swings the ball to Terry. Robinson throws on the breaks, but Terry doesn’t shoot. Instead, he drives past Robinson, forcing Noah to try to cut him off.

Now Noah is completely out of position to defend Pierce. His back is turned, and his help is either stuck in the post defending Garnett or already beaten by Terry. Pierce gets a good look at a three and he hits every side of the rim before converting it.

Having watched the success of this play once, the Celtics decided to try it again. This time, it was much simpler because Noah does exactly what Boston wanted him to do the first time. Here’s the play. Don’t be too alarmed by Jeff Green bringing the ball up the floor. He passes it off pretty quickly, I promise.

These plays are almost hilariously similar in the way they begin. Terry to Pierce with his back to the basket near the 3-point line. Celtics overload the weak side. Garnett feigns disinterest, then comes sprinting over to set a screen. Butler, once again, switches and gets backed into the post by Garnett.

But this time, Noah’s defensive decision is a little bit different. Instead of trying to cover two players at once, he aggressively denies Pierce the opportunity to shoot and tries to use his larger, longer body to deny Pierce a passing lane to Garnett as well.

Unfortunately for Noah and Chicago, the ball-denial doesn’t work. Pierce gets the ball to Garnett (who also has better position than last time), and Noah is a long ways away from helping. When Garnett catches the ball, he begins to make his move against Butler. As he does so, essentially the entire Bulls roster begins to collapse around him in an attempt to deny him a shot in the paint.

A side note if I may. I mean this in the most complimentary way possible: The Bulls are like a hive-mind and they creep me out. Every movement, every rotation is so in-sync and so scripted. They are an amazing team defensively. Good teams with good strategies can crack them, but they make life difficult.

Anyway, Boozer starts to come over to help along with every other Chicago player (including Noah), but before Boozer or any other defender can get there, Garnett has already elevated over Butler and converts a fairly easy jumper.

These plays ended up being the deciding factor Boston, and they were excellent examples of how Doc can read a defense and draw up effective sets on a case-by-case basis.

One final note: Chicago hides Carlos Boozer’s mediocre individual defense very effectively. While one could make the argument that he should have been quicker on his rotation to help Butler in the second set, it’s hard to blame him for staying attached to Bass when Bass was that close to the hoop. The Celtics beat the Bulls defense by beating arguably their best individual defender (Noah). That’s pretty impressive.

Follow Tom on Twitter: @Tom_NBA.