This is why they bought him. Three weeks ago, Juventus were staring into the abyss. Outplayed and outclassed at the Wanda Metropolitano by Atlético de Madrid, the Italian champions looked a spent force, toiling in their attempts to bring home a first UEFA Champions League in 23 years.
Even Ronaldo looked defeated, so ruthless and organised were Atlético that night.
But you should never write him off. Especially in the Champions League.
Now 34, the Portuguese forward may not be as fast as he once was, but remains as clinical as ever. His hat-trick – comprised of two headers and a late penalty – lifted Juve from a desperate position and into the last eight of the Champions League.
It's worth noting that, going into Tuesday night's game in Turin, Ronaldo had only struck once in Europe this season, but even that was against his former side Manchester United.
Ronaldo's hat-trick, however, keeping alive Juve's European dream, provided further evidence that he is football's ultimate big-game player.
He stretched his lead over Lionel Messi as the Champions League's all-time leading goalscorer, with 124 to the Argentine's 106. It was also his eighth hat-trick in the competition, bringing him level with Messi.
Ronaldo has scored 417 league goals across his career but the Champions League is where he has cemented his place as one of the game's greats.
He has now been directly involved in 76 goals in 77 knockout games (62 goals, 14 assists). It's perhaps the most staggering statistic of all; proving that he has delivered for Manchester United, Real Madrid and now Juventus over such a long stretch. He's done it in the round of 16s, quarter-finals, semi-finals, finals and in extra-time of finals.
His knockout form shows no sign of dwindling either. 18 goals in his last 14 knockout appearances prove that.
Of course, for Juventus, it was a case of 'if you can't beat him, buy him.' Ronaldo had scored ten goals in seven appearances against the Bianconeri while he was at Real Madrid, including two in 2017's final in Cardiff and three in the two quarter-final legs between the sides last season, including a spectacular overhead kick at the Allianz Stadium.
That night, Juventus applauded Ronaldo off the pitch out of respect for an esteemed adversary. This time, they cheered him as one of their own.
Spare a thought for Atlético, though. Diego Simeone's men will be disappointed at how the tie turned out, especially given their brilliance in the Spanish capital three weeks ago.
Like Juventus, they have come agonisingly close to realising their European dream. And like Juventus, they too know what it feels like to have victory snatched away by Ronaldo.
He has scored 25 goals in 33 career appearances against Atleti. Many of those have come in domestic competition in Spain, but he has made a habit out of crushing them on the European stage.
In fact, Atlético have been knocked out of every Champions League knockout stage they have been in since 2013/14 by a team containing Ronaldo. He scored in the final against them in 2014 and dispatched the decisive spot-kick in the shootout two years later, sealing Real's 11th European crown.
The following season, he inflicted more pain on Simeone, scoring a hat-trick in the semi-final as Real went on to meet Juventus in the 2017 showpiece. He scored twice in that game too.
And Juventus have seemingly figured out the key to harnessing Ronaldo's big-game prowess; rest.
Although he remains a supreme athlete, he has clocked up an enormous amount of mileage in his 16 years in the professional game. In fact, he is just a dozen away from 1,000 official appearances.
And Juve boss Massimiliano Allegri was mindful of how R&R can benefit a player like Ronaldo. Allegri has played the Portuguese as much as possible in Serie A and, to his credit, it has worked, with the No.7's 19 goals helping to establish an unassailable 18-point lead at the summit.
Now, with an eighth successive Scudetto seemingly wrapped up, Allegri chose to rest Ronaldo for Friday night's win over Udinese. It seems highly likely he will deploy a similar strategy during the remainder of Juve's Champions League campaign.
And a rested, full recharged Ronaldo is something no team wants to come up against in the quarter-finals. After the game last night, his former teammate, Rio Ferdinand, described him as a 'footballing God'. It's difficult to argue with that assertion.
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