Juve’s Claudio Marchisio (right) blocks the way for Ibrahim Afellay, of Olympiakos, at the Juventus Stadium, on Tuesday.

Juventus coach Massimiliano Allegri finally took the plunge and switched to a four-man defence for Tuesday’s Champions League match against Olympiakos Piraeus and was rewarded with a 3-2 comeback win which revived their campaign.

Allegri took over in July and, rather like a man who had been asked to look after a delicate vase, handled his new team with extreme care, clearly wary of smashing the winning formula he inherited from predecessor Antonio Conte.

That included maintaining the three-man defence which was favoured by Conte, even though it was a formation which Allegri himself had avoided using at his previous clubs.

However, with the goals drying up in Serie A and with midfielders Andrea Pirlo, Arturo Vidal, Claudio Marchisio and Paul Pogba all available, Allegri decided it was time to switch things around.

Stephan Lichtsteiner and Kwadwo Asamoah, who previously played on the flanks of a five-man midfield, were moved to the full-back positions with Giorgio Chiellini and Leonardo Bonucci in the heart of the defence.

Allegri brought in a diamond formation in midfield with Pirlo in his favoured role as a deep-lying playmaker, Vidal on the right, Marchisio on the left and Pogba given a more attacking role in the Group A match.

Juventus, who had failed to score in their last two Champions League outings, looked far more incisive than in recent games, although they still suffered from their old failing of conceding goals from set pieces.

Two goals in a minute midway through the second half saw them overturn a 2-1 deficit after Pirlo celebrated his 100th Champions League appearance with a trademark free-kick. An own goal brought them level before Pogba got the winner.

“We had the option to play a three-man defence, but I wanted to change system and try to get the best out of our central midfielders, particularly with Alvaro Morata up front,” said Allegri.

“My team played the new system well. We had good intensity in our game and created lots of chances.

“We fell behind without even realising it, but that’s football and you’ve got to remain calm and the lads did that to turn the game around again.”

Allegri said he had been wary of making changes too quickly.

“I didn’t want to create uncertainty by getting too far away from the way they played last year. But this week I was determined to change,” he said.

Allegri said the Olympiakos goals by Alberto Botia and Delvin Ndinga, in particular the first, were down to bad defending rather than difficulties in adapting to the new formation.

“The goals we conceded weren’t because we were defending with a back four,” he said.

“The first goal was unbelievable, we conceded from a header off a low cross. That’s hard to take.”