Ronaldo has been allowed to make the present era of the competition his own personal plaything but on a crisp, spring evening in the Dutch capital he found the future much less malleable.
Juventus' Portuguese forward Cristiano Ronaldo reacts during the UEFA Champions League first leg quarter-final football match between Ajax Amsterdam and Juventus FC at the Johan Cruijff ArenA in Amsterdam on April 10, 2019.
However, Brazilian winger David Neres conjured a stunning equaliser nearly immediately after half-time to give Ajax a draw that was the very least they deserved.
"We had to slow the game down". Juventus almost won it when Douglas Costa hit the post in the 85th.
"Ronaldo showed that he is on a different level".
Ronaldo was returning from a two-week injury layoff.
"CR7, Golden Head", headlined Gazzetta Dello Sport and said it was "a new masterpiece" by the 34-year-old who extended his record goal tally to 125, exactly 12 years after his first one in the competition.
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Zidane won three straight Champions League crowns with Madrid before abruptly resigning following their 2018 triumph in Kiev. That is after reports that the France international's relationship with United boss Ole Gunnar Solskjaer is deteriorating.
Ajax boss Erik Ten Hag was hoping for more but will take confidence from the last round, when his side lost the home leg to Real Madrid only to stun the holders 4-1 at the Bernabeu.
Once confirmed, this will be Allegri's fifth - but the ex-AC Milan manager said he wants the players to remain focused on the clash with Ajax even if the title is secured away to SPAL.
Ajax certainly should have scored in the 25th minute when Dusan Tadic set up Donny van de Beek, but his shot went agonisingly wide.
His side are also through to the final of the Copa del Rey, where they will face Valencia, while winning at Old Trafford gives the Catalan club the advantage over United in their bid to lift the Champions League for the first time since 2015.
Brazil global David Neres scored on the other side of the break with a superb curling effort.
Juventus only displayed their attacking threat in patches, with Federico Bernardeschi lively and Ronaldo hooking one chance wide. Neres robbed Cancelo by the left touchline just inside the Juventus half and advanced before curling a shot beyond Szczesny and into the far corner.