Juventus played in the Champions League final two years ago, so the fact that they are in the semifinals this time around isn't a complete shock. They're one of Europe's top teams. But the core of that team that went to the final in 2015 left -- Paul Pogba to Manchester United, Arturo Vidal to Bayern Munich and Andrea Pirlo to New York City FC.
While The Old Lady were left with plenty of great players, rebuilding an entire midfield -- especially one that magnificent -- is no small task. It takes some shrewd work on the transfer market and some creative managerial work.
The latter was especially true for Juventus.
Juve couldn't play with the same system anymore. They had to create new roles, develop a new system, and then somehow find a way to make it work with a group of players that, to be frank, were not natural fits with each other.
Massimiliano Allegri took more than a year tinkering with his team and trying to get it right. Finally, it looked like everything was starting to come together, though.
They put Paulo Dybala underneath Gonzalo Higuain, with Sami Khedira and Miralem Pjanic in the central midfield. Juan Cuadrado nicely slotted on the right wing, too.
The only remaining hole was on the left wing, but there was a problem -- they didn't have a single natural winger to put out there.
So that tapped Mario Mandzukic.
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Mandzukic had never really been a winger before. He was an out-and-out striker, and a damn good one at that. Higuain's arrival pushed him to second choice up top, but he was (and still is) plenty good enough to be a striker for an excellent team.
Moreover, this wasn't the first time Mandzukic had been asked to play on the wing. Bayern Munich tried it when the Croatian was there and it went astonishingly poorly. He wasn't a good fit, made little impact and was openly upset with the move.
There was little reason to think that Mandzukic would work out wide.
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And yet, Mandzukic has been brilliant on Juventus' left wing.
The Croatian has just eight goals this season -- his lowest output since 2006, when he was a 19-year-old playing for NK Zagreb in his first professional season -- but his game has been about much more than just goals. Whereas that is how he was judged as a striker, now Mandzukic's worth takes a little deeper look.
Mandzukic has been terrific in possession, helping move opposing defenses and create spaces for his teammates. He's also been quick to make runs that have made it so Dybala has space to operate in the center of the pitch, not to mention occupying defenders that would otherwise be harassing Higuain.
Add in four assists and you have someone who has been integral to Serie A's top team that is also into the Champions League semifinals.
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Nothing has been more surprising than the work Mandzukic has done defensively, though.
As is usually the case, Juve lean on their ability to keep goals out and it takes all 11 players to do it. While the back line is rightfully lauded, the way the front line presses, takes away passing lanes, and then tracks back to minimize space and collect second balls on clearances, is equally important.
A converted striker playing on the wing, and a big body who isn't a speed demon by any stretch, he isn't the type of player you would expect to be a defensive force on the wing, but Mandzukic has been just that. Working with Alex Sandro, Mandzukic has helped shut down the entire wing and you'll often see teams completely give up attacking down the flank because they can't find a way through there.
Most of the talk about Juventus revolves around Dybala, who looks like the next great creative player. And he deserves all the accolades he's been getting. Higuain, while incredibly expensive, has been bagging goals left and right to make Juventus' purchase look wise, too. And with a who's who of Italian defenders in front of Gianluigi Buffon, there is no shortage of praise for Juventus' defense.
As a result, Mandzukic is often out of the spotlight. Unless he bags a handful of goals in the Champions League semifinals, he may not get a single headline. But Juventus are not into the final four without him. They're not eyeing another final and they aren't, well, functioning.
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Juventus have rebuilt their team over the last year and a half to get back among Europe's elite. And as good of a job as Allegri has done to make all the pieces fit, there was no logical piece on the left wing. There wasn't even an actual winger. But there was Mandzukic, someone who had no business making it work out there and has instead become Juventus' unsung hero.
Maybe he'll be the one to put Juventus over the top and capture the Champions League, too. Not even 2015 Juventus could do that.