* Tonight on TNT: Warriors vs. Celtics (8 ET)

While teams with more continuity are still trying to figure out their identity, the Boston Celtics — the team that returned only four players from last season’s roster and lost one of its best players five minutes into the season — have the best record in the league.

The only games the Celtics have lost have were the game in which Gordon Hayward broke his ankle and the game they played the following night. There have been some close calls along the way (10 of their 15 games have been within five points in the last five minutes), but Boston is taking a 13-game winning streak and the league’s best defense into the most anticipated game of the early season.

The Golden State Warriors are bringing their own streak — seven wins by an average of 19.8 points — to TD Garden for the first the first game of tonight’s TNT double-header.

CELTICS BASICS

Pace: 98.9 (22nd)

OffRtg: 103.6 (19th)

DefRtg: 95.8 (1st)

NetRtg: +7.8 (2nd)

CELTICS LINKS

Team: Per game stats | Advanced splits | Lineups | Game log

Players: Per game stats | On-off court | Player shooting

History: Season by season results | Advanced stats | Franchise leaders

THE STAT

The Celtics are the only team that, vs. the league average, has improved in regard to each of the four factors on defense.

THE CONTEXT

Celtics opponents are shooting worse, getting to the line less often, turning the ball mover more and grabbing fewer offensive rebounds than they did last season. The Los Angeles Lakers can say the same, but their increase in opponent turnover rate (+0.8 turnovers per 100 possessions) is less than the league average (+1.4).

On both ends of the floor, shooting is the most important thing. The Celtics’ No. 1 ranking on defense starts with having the lowest opponent effective field goal percentage.

And the key to that has been on the perimeter. The Celtics rank second in opponent field goal percentage from mid-range and fourth in opponent 3-point percentage.

On top of that, their opponents have taken only 31 percent of their shots, the sixth lowest rate in the league, from 3-point range. And on top of that, only 19 percent of their opponents’ 3-point shots, the fifth lowest rate, have come from the corners. So not only have the Celtics defended 3-pointers well, but they’ve done well in preventing them and preventing the more effective ones.

Through Wednesday, the league has shot 38.6 percent on corner threes and 35.7 percent on above-the-break threes. That difference (2.9 percent) is a little less than what it’s been over the past five seasons.

This is the seventh straight season in which the league has taken a greater percentage of its shots from 3-point range than it did the season before. The Celtics’ defense is one of nine that has reduced the percentage of its opponents’ shots that have come from beyond the arc from last season to this season.

Of course, the Celtics ranked fifth in opponent effective field goal percentage last season, with their 3-point defense being an important factor. Amazingly, if they stay there, this would be the 11th straight season that Boston has ranked in the top five in opponent 3-point percentage, a stretch that began with their 2007-08 championship season.

While they’ve seen the league’s third biggest drop in opponent effective field goal percentage, it’s been the other areas of defense where the Celtics have gone from below-average last season to above-average this season, with rebounding being the most remarkable turnaround.

Al Horford has grabbed 24 percent of available defensive rebounds, his highest rate since his second season in the league and up from 18.3 percent last season. But the Celtics’ rebounding improvement goes beyond Horford.

Avery Bradley is a good rebounding guard, but the Celtics’ starting shooting guard this season (Jaylen Brown) has a higher defensive rebounding percentage (17.6 percent) than Bradley did last season (16.1 percent). The same goes for Kyrie Irving (8.8 percent) and Isaiah Thomas (7.0 percent).

Last season, the Celtics’ starting backcourt was 5-foot-9 and 6-foot-2. This season, their starting backcourt is 6-foot-3 and 6-foot-7. At small forward, Jayson Tatum (6-foot-8) is bigger than Jae Crowder (6-foot-6). That’s a big difference in height on the perimeter and it makes a big difference in every aspect of defense, not just rebounding.

This defensive improvement is coming with a 21-year-old (Brown) and a 19-year-old (Tatum) leading the team in minutes. But size has turned out to be more important than age.

Bigger bodies and longer arms will obviously shrink passing lanes and create more turnovers. More important, the Celtics’ added size allows them to more liberally switch screens. That has allowed them to more often keep the ball in front of them and stay out of rotation, which helps them do a better job of defending the 3-point line, avoiding fouls, and rebounding.

“That’s a huge thing that everybody wants to be able to do,” Celtics coach Brad Stevens said Tuesday. “We’ve put a huge premium on it, obviously, in drafting Jaylen, Jayson and Semi [Ojeleye]. Those guys all can guard multiple positions.”

Switching is easier said than done. It requires constant communication. And no team will test the Celtics’ ability to switch successfully more than the Warriors will tonight. Golden State has seen and beat every kind of defensive scheme.

Golden State is also a challenge, because the Celtics’ defense has been best when they’ve have played biggest. They’ve allowed a ridiculously low 84 points per 100 possessions in 131 minutes with Al Horford and Aron Baynes on the floor together. But Stevens has been willing to go with different looks to start games when the matchup has dictated it. Against Brooklyn on Tuesday, Marcus Morris started and Baynes played just 12 minutes.

The Celtics haven’t had the toughest schedule in regard to opponent offensive strength. Thursday’s game against Golden State will be just their fourth against a team that currently ranks in the top 10 in offensive efficiency. They’ve played twice as many games against the bottom 10 (six) as they have against the top 10 (three). Time will tell if the defense can remain as stout as it has been through the first four weeks of the season.

“Maybe we’ve just done some good things early and we’ll taper off,” Stevens said. “And maybe we won’t.”

THE VIDEO

Here’s an after-timeout possession from Tuesday where Brooklyn sets a double-pin-down screen for Allen Crabbe, who slips a screen for Spencer Dinwiddie.

The ever-alert Horford sees Crabbe (the No. 2 3-point shooter in the league last season) break free and switches out. Brown switches onto Horford’s man (Trevor Booker) but then switches again with Marcus Morris when Booker heads to the paint. Brown then switches with Irving on a Spencer Dinwiddie-Rondae Hollis-Jefferson ball screen, Tatum and Morris switch off the ball in the right corner, and Brown ultimately contests a Dinwiddie three with four seconds left on the shot clock.

• NBA.com/stats Video: Watch Charlotte shoot 6-for-22 from 3-point range (with only one attempt from the corners) against the Celtics on Nov. 10.

TWO MORE CELTICS NOTES

1. The Celtics have scored 111 points per 100 possessions in the second half of games.

That ranks as the league’s second best second-half offense and is an increase from the 96 points per 100 possessions (third worst) the Celtics have scored in the first half of games.

In the first half, the Celtics have scored at the rate of the third worst offense in the league. In the second half, they’ve scored at the rate of the second best offense.

Overall, the Celtics rank 19th offensively, having scored 5.0 fewer points per 100 possessions than they did last season (when they ranked eighth). Only two teams (Sacramento and Utah) have seen a bigger drop in effective field goal percentage from 2016-17 to ’17-18, and no team has seen a bigger drop in the percentage of its shots that have come from 3-point range (from 39.3 percent to 35.5 percent).

Horford and Irving have actually shot slightly better in the first half of games. But almost every one of their teammates has shot much better in the second half.

Both their 3-point percentage and the percentage of shots they have taken from 3-point range have been higher after halftime. They’ve also cut down on turnovers and gone to the line more often in the second half of games.

The Celtics’ defense has been good enough in the first half that they haven’t fallen into many holes; They’ve trailed only three of their 15 games by double-digits. But their defense has also been better after halftime.

Amazingly, the Celtics’ third-quarter NetRtg of plus-25.0 points per 100 possessions doesn’t lead the league. The team they’re playing on Thursday has outscored its opponents by 28.2 points per 100 possessions in the third.

2. Jayson Tatum has shot 19-for-35 (56 percent) on catch-and-shoot threes..

That’s the second best mark among 157 players with at least 25 catch-and-shoot 3-point attempts, trailing only that of J.J. Barea (20-for-32).

Tatum has also shot a solid 42 percent on shots between the restricted area and the 3-point line. His restricted area field goal percentage (56 percent) is below the league average, but he’s made up for that by getting to the line 41 times for every 100 shots from the field. That free throw rate ranks 19th among 157 players with at least 100 field goal attempts.

Tatum’s effective field goal percentage of 57.9 percent ranks 25th among that same group (just a tick behind that of Stephen Curry) and is pretty remarkable for a rookie that plays on the perimeter. In fact, only one guard or small forward has shot better on at least 500 shots over his full rookie season.

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

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