And Ajax are in a commanding position after the first leg against Spurs as Donny van de Beek's composed finish past Hugo Lloris means Erik ten Hag's side have a one-goal lead going into the second leg in Amsterdam.
Juve head coach Allegri thinks they've been fortunate at times in this season's competition, however, pointing to some of the players that were missing from his starting XI for the 2-1 defeat to the Dutch side on April 16.
The likes of Giorgio Chiellini, Mario Mandzukic and Douglas Costa missed out on that occasion, with Allegri also discussing how both Harry Kane and Heung-Min Son were absent for Tottenham on Tuesday night.
Jan Vertonghen also had to be substituted after a nasty clash of heads with Toby Alderweireld and former AC Milan boss Allegri believes that there have been moments in the Champions League where everything's gone right for Ajax.
He Sky Sport Italia: "In the Champions League there are moments when everything goes right, Ajax faced us without us having five players.
"Then they go to London and they [Tottenham] were missing the [main] striker [Kane], and the other striker [Son] is banned. After 15 minutes the central defender [Vertonghen] gets injured..."
Allegri also discussed Liverpool's 3-0 defeat to Barca, believing that the Catalans have better players than their opponents that ultimately made the difference on the night.
He added: "Liverpool had three big scoring chances [against Barcelona], but Barcelona had four and scored three. Why? Because their players are of a higher level and make the difference in certain situations.
"Barcelona has players accustomed to that level and they proved it on the night, regardless of whether Liverpool had a good game or not. It's like a race. Everyone can run the first 900 metres but very few can run the final 100."