There was one possession in Toronto's win over Philadelphia earlier this season that showed how the Raptors have been able to build the second-best defence in the league despite losing two elite defenders in Kawhi Leonard and Danny Green in the offseason.

Welcome to "One Possession!" Throughout the 2019-20 NBA season, our NBA.com Staff will break down certain possessions from certain games and peel back the curtains to reveal its bigger meaning.

Today, the Toronto Raptors' defence takes the spotlight.

Context: On January 22 of this season, the Raptors secured their fifth straight win by limiting the Philadelphia 76ers to 95 points on 38.1 percent shooting from the field. The 76ers jumped out to a quick start with a 35-point first quarter, but the Raptors put the clamps on them the rest of the way to come up with the victory.

The possession: Following a made basket from Pascal Siakam that extended Toronto's lead to six points with just over three minutes to play in the fourth quarter, the Raptors got a much-needed stop on Al Horford. Here's the possession:

Breakdown: The five Raptors on the court are Siakam, Kyle Lowry, Fred VanVleet, Norman Powell and Serge Ibaka. They fall back into a man-to-man defence following Siakam's basket, with Siakam guarding Ben Simmons, Lowry guarding Matisse Thybulle, VanVleet guarding Furkan Korkmaz, Powell guarding Tobias Harris and Ibaka guarding Horford.

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Shortly after Simmons crosses halfcourt, Harris moves towards him as though he is going to set a screen, but Simmons kicks a pass to Horford on the opposite wing before Harris can make contact with Siakam.

Before Simmons makes the pass, Ibaka motions to VanVleet to switch onto Horford.

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Although VanVleet doesn't have the size to guard Horford, it allows Ibaka to stay on the baseline, where he is better positioned to provide help in case someone on the 76ers gets into the paint.

Rather than looking to shoot over VanVleet, Horford passes the ball to Korkmaz in the corner.

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Korkmaz takes one dribble towards the basket, but Ibaka is able to keep him in front of him. Instead of forcing the issue, Korkmaz retreats to the corner while Horford wisely makes his way to the block to establish himself in the post with VanVleet guarding him.

Horford only ranks in the 42nd percentile with 0.90 points per post-up possession this season, but he has the tools to punish someone like VanVleet with his back to the basket, whether it's by bulldozing his way into the paint or drawing a double team and finding the open man.

In other words, it's a pretty clear mismatch.

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However, before Horford can get there, Siakam and VanVleet execute a well-timed switch to give the Raptors a more favourable matchup.

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There's only eight seconds remaining on the shot clock when Horford receives the ball. He faces up to the basket and looks for a pass, but with the Raptors in perfect help position, he's left with having to create a shot for himself against Siakam with time ticking away.

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Why it matters: This possession gives some insight into how the Raptors have been able to build the second-best defence in the league despite losing two elite perimeter defenders in the offseason in Kawhi Leonard and Danny Green.

It begins with Siakam picking up Simmons in semi-transition, where the one-time All-Star is at his best. Because Siakam has the size and speed to match up with him, Simmons isn't able to score a quick basket, forcing the 76ers into their halfcourt offence, where he's far less of a scoring threat.

From there, the 76ers look to punish the Raptors for having VanVleet on Horford, only to have Toronto blow it up by switching Siakam onto Horford.

MORE: Nine thoughts from Toronto's win over Philadelphia

It speaks to Siakam's versatility as a defender that he can transition from guarding Simmons to Horford without it being a clear mismatch. Simmons is obviously not a traditional point guard even though he functions as Philadelphia's point guard on offence, but the list of players who can guard as many positions as Siakam isn't very long. It includes the likes of Kawhi Leonard and Giannis Antetokounmpo, plus LeBron James when he's locked in.

The timing of that switch is important. Had VanVleet and Siakam done it a split-second sooner, Horford may have been able to sneak his way to the basket on the cut. Had they done it a split-second later, Horford may have gotten deeper post position, setting him up for a much better shot than he ended up getting.

What goes on on the other end of the court is also important because the Raptors execute another switch when Horford catches the ball, this time moving Lowry onto Simmons and VanVleet onto Thybulle. While Lowry isn't much bigger than VanVleet, he's one of the stronger players at his position, giving him a better shot of keeping Simmons out of the paint.

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That's three switches in seven seconds, each done for a different purpose - the first to keep Ibaka as close to the basket as possible, the second to keep Horford out of the paint, the third to keep the 6-foot-10 and 240-pound Simmons off the offensive glass.

It might look simple when broken down, but there aren't many teams whose rotations are as smart and crisp as Toronto's. Raptors head coach Nick Nurse deserves a lot of credit for that, not only for installing the system that he has, but for getting the most out of every player, from Lowry and Siakam at the top of the depth chart to Rondae Hollis-Jefferson and Chris Boucher further down.

Whether or not it can fuel another deep playoff run remains to be seen, but it gives the Raptors a fighting chance against any team in the league because no task ever seems too great for them on that side of the court.

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