Trailing 3-0 after a chastening home defeat a week ago, Juventus headed to the Santiago Bernabeu needing to emulate the miraculous comeback of Serie A rivals Roma against Barcelona the previous night.
And Mandzukic gave Juve the perfect start when he opened the scoring inside the first two minutes in the Spanish capital.
The Croatian, who scored a memorable overhead kick in last season’s Champions League final defeat by Madrid, headed home Sami Khedira’s cross from the right-hand side.
In doing so, the 31-year-old scored the quickest goal Madrid have conceded at home in the Champions League, with the effort being timed at 76 seconds.
Mandzukic further fuelled hopes of a stunning turnaround for Juve when he doubled the Italian champions’ lead eight minutes before half-time.
Again demonstrating his aerial prowess, Mandzukic rose above Dani Carvajal to meet Stephan Lichtsteiner’s cross and head beyond Keylor Navas.
It meant that Mandzukic became the first player to score two first-half goals for the away team in a Champions League tie at the Santiago Bernabeu.
2 - Mario Mandzukic is the first player to score two first-half goals away at the Bernabeu in a Champions League match. Fighting. #RMAJUVE— OptaJoe (@OptaJoe) 11 April 2018
His double also took his ratio of headed goals in the Champions League to 50 per cent of his overall total, with 10 of his 20 coming via that route.
Madrid also headed into the break on the end of a rare scoreline as it was the first time they had trailed by two goals at home in the Champions League since February 2000 when they were losing to Bayern Munich.
The La Liga giants went on to lose that match 3-1, with Zinedine Zidane responding to his team's poor start this time around by replacing Casemiro and Gareth Bale with Lucas Vazquez and Marco Asensio at the interval.