When Antonio Conte arrived at Chelsea last summer, he faced near-daily questioning over whether he would employ a 3–5–2 formation at his new club. The shape had become his trademark after success with Juventus and the Italian national team — but three at the back was still a rare sight in England, where four defenders was canon and any numerical variation happened farther up the field.

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Initially, Conte maintained that he would test a number of shapes in search of whatever configuration would take Chelsea from 10th place back to the top of the table. It began with a highly structured 4–2–4 in preseason, but that led to less-than-spectacular results. Come the start of domestic play, Conte shifted toward the more widely used 4–2–3–1 and 4–3–3.

Like with the 4–2–4, though, Chelsea’s early performances in the 4–3–3 were flawed. The spacing was often nonexistent, and the shape was disconnected both vertically and horizontally, resulting in a dysfunctional attack and a porous defense. An easy opening schedule obscured Chelsea’s issues until they were exposed in back-to-back defeats against Arsenal and Liverpool.

You probably know the story by now: Conte switched to a 3–4–3, and since then Chelsea have won 14 games, lost one, scored 35 goals, and conceded just six. They’re atop the table, seven points clear of Tottenham and Liverpool, and it’s going to take something special — like, say, the venerated tradition of Chinese football — for anyone to catch them.

We can draw a straight line from Conte’s tactical tinkering to Chelsea’s ascent, but the players deserve just as much credit. The most fascinating aspect of Conte’s formation change isn’t the switch to three at the back; it’s the move to only two in the center of midfield. Over the past decade, most top teams have opted for three central midfielders in order to dominate possession in the most important part of the field. All of Chelsea’s top-six rivals field a trio, but Conte has opted to play a man down in the middle. So why does it work? N’Golo Kanté and Nemanja Matic can do the job of three men.

While creative winger Riyad Mahrez and the pacey striker Jamie Vardy led Leicester City’s title-winning attack last year, Kanté was doing just about everything else. The ultimate auxiliary player, he was an active member in both defense and attack, complementing his more attacking-minded midfield partner, Danny Drinkwater, in their 4–4–2.

Kanté was the standout defensive performer on an excellent defensive team. At Leicester, he often played the role of two midfielders through his immense ability to cover space.

Much of the same can be said of Matic’s game. Standing at 6-foot-4, his ability to cover ground is more due to his giant stride than Kanté’s boundless energy. But he reads the game just as well and is an even better passer, thanks to a brilliant understanding of space and sound technique.

Within a midfield trio, the roles are typically distributed evenly among a destroyer, a supporting passer or box-to-box player, and a creator. But Kanté and Matic fulfill all of those roles — and then some. Kanté is a box-to-box destroyer, and Matic, who has six assists on the season, is a destructive creator.

Of course, while Kanté and Matic are flourishing despite a numerical disadvantage, they’ve also been aided by Conte’s system. Chelsea are more dominant than they ever were with an extra midfielder; efficiency overcomes numbers. In their 4–3–3, Conte’s club were unable to control the game due to a lack of spacing. The front three would become stretched, and the nominal attacking midfielder, Oscar, who’s now playing in China, would often drop too deep to get the ball, leaving a chasm of space between the midfield and the attack.

Now, everything is linked so much better. Their average positions often look like a tactical chalkboard:

During buildup in the 4–3–3, both Matic and Kanté were required to play deeper to help bring the ball out from defense into midfield. But now, neither has to drop in, as the additional third center back allows Chelsea to overload most opposition presses.

With wingbacks pushed up alongside the midfield, both wingers are able to move inside, filling the gap between the midfield and the attack. Eden Hazard, especially, has benefitted from a role that allows him greater freedom in the final third.

With more links through the attack, everything clicks. Chelsea are passing the ball much more cleanly, and their switches of play are faster and more dangerous. Kanté and Matic are no longer faced with the task of bridging a chasm of space. Instead, like hockey defensemen, they can focus on supporting the attacks by maintaining ball circulation and connecting their team from one wing to the other.

The tactical shift also allows Matic and Kanté to play a vital role during the game’s crucial moments: right when possession is lost.

When Chelsea are attacking the opponent’s penalty area, Matic and Kanté are joined by a center back to form a chain to cover any potential counterattacking routes. (These particular spaces have been identified by Borussia Dortmund coach Thomas Tuchel as the spaces where 90 percent of rebounds and clearances end up.) The three of them can cover the entire width of the pitch, making it almost impossible for the opponents to catch Chelsea off-guard.

The increased resistance against counterattacks, coupled with a back line that becomes a five-man wall as the wingbacks drop in when Chelsea loses the ball, has created the best defense in the league by expected goals. Matic and Kanté fortify the center, but if they’re bypassed, there are three center backs behind them. And if the ball goes out wide, there’s a wingback and an extra center back to provide cover. It’s a system filled with fail-safes.

In recent years, teams like Leicester City and Atlético Madrid have shown that it’s possible to build an elite defense with two central midfielders. What no one has done, however, is dominate in possession with just two. Although Chelsea’s possession rate of 54 percent isn’t out of the ordinary, no team attains the same level of control with the ball. Thanks to the diverse abilities of the men in the middle, they’ve paired a goal-stopping behemoth with one of the Premier League’s most efficient attacks.

There aren’t many other midfielders who could function in Conte’s current system — Luka Modric, Toni Kroos, and maybe a handful of others — but without Conte’s system, Kanté and Matic also wouldn’t be functioning as spectacularly as they currently are. “When I was in Italy I liked to say, no, that the manager, the coach is like a tailor,” Conte said during his presentation in July. “A tailor who must build a dress, the best dress for the team.” It took him six games, but the Chelsea manager seems to have found the right clothes.

There’s still plenty of time left in the season, and Chelsea have become more reliant on a specific starting 11 than any other team in England — except, with no European football and 14 wins out of 15, can you blame them? Injury luck is sure to play a part in how the rest of the Premier League campaign shakes out, but the math remains in Chelsea’s favor: As long as Kanté and Matic stay healthy, one plus one will equal three.