Ajax settled well after that but, despite not playing well, Juventus went ahead when Ronaldo got away from the defenders to score the 126th Champions League goal of his career.
The second was largely thanks to a blunder by David de Gea.
One of the best goal-keepers in the world, he is known to be United's best line of defense.
Ajax enjoyed the greater possession, which Juve were happy to concede though fortunate to just relinquish a single strike, the net and goalkeeper Wojech Szczęsny peppered by a disproportionate amount of shots by a team that has already scored 106 goals in the Eredivisie.
Whatever be the circumstances, one can't rule Lionel Messi out.
"Can we can go on to win the competition?"
He proved once again that he can be relied upon any time, besides making his case stronger for this year's Ballon d'Or.
"Winning five Scudetto is not easy, reaching two Champions League finals, is not easy". "We promise this season we will do all we can to bring that attractive cup back to Camp Nou".
Signing the competition's leading scorer of all time seemed like a very good way of getting over that 23 years without the title but on Tuesday they were beaten 2-1 at home by Ajax and crashed out at the quarter finals stage.
Juventus are still set to clinch an eight successive Serie A title as they sit 17 points clear at the top of the table.
Other clubs must be wary of Ajax.
United had arrived at Camp Nou hoping to take inspiration from its Champions League final victory 20 years ago, when current manager Ole Gunnar Solskjaer capped a comeback against Bayern Munich by scoring the victor in injury time.
The first leg saw 5 cards dished out and I'm tipping a similar outcome tonight, especially given the French referee Clement Turpin has been dishing out cards for fun in this years UCL.
CR7 did all in his powers to guide Juventus to a victory, he needed support, which was missing.
Barca, though, remain keen to respect the protocol put in place by Ajax, who still have a lot to play for this season and want their players to remain focused on sporting objectives.
But they have now come back down with a bump after Max Allegri's team exited Europe's premier club competition - which they last won in 1996, when they beat Ajax in the final.