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Walter Mazzarri has given Inter Milan a much-needed blessing this season—stability in the manager's office.

Since Jose Mourinho left Inter after his 2010 treble to coach Real Madrid, the club's hot seat has been a revolving door. His immediate successor, Rafael Benitez, didn't last until the end of the winter break in 2010. He was replaced by former Milan coach Leonardo, who led the team to a solid runner-up finish before leaving to become sporting director at PSG.

Gian Piero Gasperini lasted all of five matches (literally) before being run out for Claudio Ranieri, who was in turn fired later in the 2011-12 season and replaced by Andrea Stramaccioni. Strama led Inter to a strong finish and was considered a rising star—until last year's dismal failure that can squarely be blamed on the young coach's tactical indecisiveness.

Inter was looking for their sixth manager in the space of four seasons when Mazzarri left Napoli this summer and came to the San Siro. He has taken a listless side and given them an identity. That Inter is now a top-five side with a virtually unchanged roster from last year's disastrous ninth-place finish proves what most already knew: Mazzarri is one of the best coaches in the Serie A.

His tactics might seem limiting. He has hardly ever deviated from his three-in-the-back mentality, whereas some other coaches—notably Antonio Conte—have switched between three and four in their defensive lines.

But Mazzarri has been remarkably subtle in changing his formations to suit the players he has at his disposal.

The 3-5-2 that is considered his bread and butter has been incredibly adaptable. There were some stone-cold constants, like the presence of Christian Maggio and Camilo Zuniga on the wings and Paolo Cannavaro in the center of the defensive line. But as personnel changed, so too did Mazzarri's tactics.

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Ezequiel Lavezzi and Fabio Quagliarella began up top with Marek Hamsik in the hole behind them. When Edinson Cavani arrived from Palermo and Quagliarella moved on to Juventus, the formation shuffled to a 3-4-3. Cavani played the centre-forward position with Lavezzi on the left side. Hamsik would drop into the midfield to help win the ball before dashing up to the right wing to link up with his linemates and help finish the attack.

Newly-arrived Gokhan Inler anchored the rear of the midfield. Napoli were a fast-paced counter-attacking side that unleashed the fury of the Three Tenors at hyper-speed.

When the Three Tenors broke up after Lavezzi left the team, a more conventional 3-5-2 returned, with Cavani partnered by Goran Pandev and fed by Hamsik—now solidly back in the midfield—and rising star Lorenzo Insigne behind setting up the play. Hamsik ended up notching 14 assists and Cavani won the title of capocannoniere.

Small, subtle tweaks in response to each personnel change and the offensive machine of Napoli still churned on.

Mazzarri has done the same at the San Siro.

Some in Milan looked at the three-man line with skepticism—Gasperini had tried to implement a similar system two seasons before with disastrous results. But unlike Gasperini, who shoe-horned players into his system with little regard for the players' own abilities, Mazzarri molded his formation to the players he had on hand.

Instead of a 3-5-2 or 3-4-3, Mazzarri has utilized a 3-5-1-1 formation for Inter. Argentinian Rodrigo Palacio serves as the tip of the spear. Ricky Alvarez and Fredy Guarin alternate between the hole directly behind Palacio and the rest of the midfield. Yuto Nagatomo plays the Maggio role, albeit on the left rather than the right. Mainstay Esteban Cambiasso holds down the midfield from deep.

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Like at Napoli, the subtle changes Mazzarri has made have brought out the best in his players. Palacio is having a career year that should see him make his way to Argentina's World Cup squad. Nagatomo has doubled his career goal total from the left wing. Alvarez has emerged as the trequartista much in the mold of Hamsik. Guarin has played so well that Chelsea is on his tail for a January transfer.

Inter is dissimilar to Mazzarri's Napoli in another way: speed. Napoli at their height were all about breakneck counterattacks. Inter is more of a possession team. Three of the team's last five games have seen them maintain at least 55 percent possession.

Mazzarri's tactics do have weaknesses. As shown in their dramatic second-leg fall against Chelsea in the Champions League two years ago, it can be vulnerable to teams with good wing play that provide quality crosses to a central striker.

He has also proved over-reliant on his own centre-forward. Last year, Edinson Cavani scored 46 percent of Napoli's goals over all competitions. This year, Rodrigo Palacio has more than twice as many goals as any other Inter player.

But weighed against Mazzarri's tactical nous, these trade-offs can be mitigated.

Mazzarri has taken a team that were in the depths of despair and given them an identity that they lacked through three years of managerial upheaval. With little in the way of player turnover, he has taken a ninth-placed team and put them in position to run for a return to the Champions League at the winter break.

It's been an astonishing run, and the vast majority of the credit goes to Mazzarri, both for the stability he has brought and the tactical moves he has made to get the best out of his players. The team's transformation has firmly entrenched him as one of the best coaches in Italy.