The Eastern Conference semifinals series between the Toronto Raptors and Boston Celtics has taken an unexpected path to an expected destination. The Celtics were half a second from taking a 3-0 lead, but we now have a 2-2 series with a pivotal Game 5 on Monday (6:30 p.m. ET, TNT).

With a spot in the conference finals coming down to three games, here are three things to know about what we’ve seen so far …

A starting advantage

The Raptors seemingly had a depth advantage coming into this series with Gordon Hayward out, Marcus Smart in Boston’s starting lineup, and legit questions about everybody left on the Celtics’ bench. The Raptors had *the NBA’s best bench in the regular season. And then they had the best bench in the first round of the playoffs, outscoring **the Brooklyn Nets by 72 points (28.4 per 100 possessions) in 116 minutes with Norman Powell and/or Serge Ibaka on the floor.

* According to aggregate (estimated) bench NetRtg.

** Necessary context: Brooklyn’s depleted bench was pretty terrible.

But through the first two games of this series, Toronto was a minus-20 in Powell and Ibaka’s 32 minutes together. With Celtics back-up center Robert Williams III shooting 10-for-10, Boston was winning the bench minutes.

Raptors note…

They were a +11 in 32.9 minutes in Game 2 w/ KL, FVV, OGA & PS on the floor w/ either Ibaka or Gasol, scoring 78 points on 64 possessions: https://t.co/UOT11RMboF

Other lineups were a -14 in 15.1 minutes, scoring 10 points on 34 possessions.

— John Schuhmann (@johnschuhmann) September 3, 2020

Through those first two games, the Raptors were a minus-1 in 64 minutes with Fred VanVleet and Kyle Lowry on the floor together and, incredibly, a minus-30 in 17 minutes with VanVleet on the floor without Lowry. The solution was simply to not let Lowry rest. The 34-year-old point guard played 46:29 in Game 3 and then 43:47 in Game 4.

He’s not the only Raptor whose minutes have been extended. Pascal Siakam has actually played the entire second half in each of the last three games. OG Anunoby played the entire second half of Game 3 (capping it with his only three points of those 24 minutes), and VanVleet played the entire second half of Game 4.

> Game 5: Celtics vs. Raptors, Monday at 6:30 ET on TNT

The Raptors’ starters have been pretty good. After getting outscored in Game 1, the Toronto starting lineup is a plus-24 in 62 minutes over the last three games. That breaks down to a plus-30 in 37 minutes against the Boston starting lineup and a minus-6 in 25 minutes otherwise.

Celtics coach Brad Stevens subbed Williams in for Daniel Theis just 2 1/2 minutes into Game 4, seemingly preferring the Williams match up vs. Marc Gasol. After playing 13 of his 50 minutes against Gasol through the first three games, Williams played 12 of his 15 minutes against Gasol in Game 4.

For the series, Boston is a plus-10 with the Time Lord vs. Big Spain matchup, and we could see more of it going forward.

The second quarter: Not pretty

That Toronto advantage with the starters has shown up more in the third quarter than in the first. While they’ve been outscored by 39 points otherwise, the Raptors are a plus-26, having scored 129.8 points per 100 possessions, in the third period.

Siakam has almost as many buckets in the third quarter (when he’s 13-for-25) than he does in the other three periods combined (14-for-45). Anunoby is 8-for-10 in the third, Ibaka has made all four of his third-quarter 3-point attempts, and the Raptors have scored at least 125 points per 100 possessions in all four third quarters.

The second quarter, meanwhile, has been brutal … on both ends of the floor. Both teams have scored less than a point per possession in all four second quarters of the series. The cumulative score in 48 second-quarter minutes is Celtics 88, Raptors 76.

This has been the least efficient of the four conference semifinals series. Through Sunday, the Celtics (104.6 points per 100 possessions) and Raptors (101.0) rank seventh and eighth in offensive efficiency in this round. The Toronto offense has improved since the first two games, while the Boston offense had its worst game of the playoffs on Saturday, with the Raptors’ defense playing a not-insignificant role in the Celtics shooting 7-for-35 from 3-point range.

It seems unlikely that either team is going to bust out with a huge offensive performance in Game 5. Maybe one could at least score a point per possession in the second quarter, though.

Celtics struggles against the zone

The Raptors played the third-most zone in the regular season, according to Synergy play-type tracking. And they’ve played more than twice as much zone in this series as they did in the first round against Brooklyn. The champs have played zone on 55 (14%) of Boston’s offensive possessions.

There have been a few possessions of a triangle-and-two zone, and in the fourth quarter of Game 4, we saw a few possessions of a box-and-one. But for the most part, the Raptors have employed a 2-3 or 2-1-2 zone. And through four games, the Celtics haven’t quite figured it out.

Boston has scored just 47 points on those 55 possessions of zone, a rate of 85 per 100 possessions. They’ve shot 15-for-42 (6-for-23 from 3-point range), with more turnovers (16) than field goals. Otherwise (in transition and against man-to-man), the Celtics have scored 108 points per 100 possessions.

The one good stretch that the Celtics had against the zone was late in the third quarter of Game 3, when they scored 15 points over eight possessions. The first of those eight was probably their most aesthetically-pleasing possession against the zone …

The Raptors’ 21 possessions of zone in Game 3 were more than they played in Games 1 and 2 combined (19). And despite the Celtics’ success in that third-quarter stretch, Toronto came back with it midway through the first quarter of Game 4 on Saturday. There was one bad breakdown (allowing a Williams dunk), but Boston scored just 13 points on 15 possessions against zone in Game 4, turning the ball over four times.

One early-fourth-quarter possession against the box-and-one included a lot of player movement, but the Raptors covered it well. And when the movement stopped, Marcus Smart committed one of those turnovers late in the clock…

The Celtics are obviously going over their zone offense in between games, but the need for rest on days off may make it hard to get in any live-action, practice reps. Expect to see more of it in Game 5.

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John Schuhmann is a senior stats analyst for NBA.com. You can e-mail him here, find his archive here and follow him on Twitter.

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