Ronaldo put Juventus in front on the stroke of half-time with a diving header to take his record goal tally in the competition to 125, only for Brazilian winger David Neres to level almost immediately after half-time to put the tie on a knife edge ahead of next week's return leg in Turin.
"Ronaldo showed that he is on a different level. His timing and movement is different to everyone else's, there's nothing you can do about it," Allegri told Sky Sport Italia on Wednesday.
"He is a player who just has a different technique than the others."
Ajax piled on the pressure at the Johan Cruyff Arena, going close on a number of occasions before Douglas Costa nearly delivered a late sucker punch for Juve when he struck the woodwork.
Their spectacular comeback from a 2-1 first-leg home defeat to Real Madrid with a thumping 4-1 win at the Santiago Bernabeu in the previous round showed that the tie is far from over.
"We were good defensively, the team was nice and compact, there is good reason to think we can get to the semi-finals.
"We are not worried, we have great respect for Ajax but you have to be ready.
"One each is better than 0-0, in Turin we will have to play to win.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)