The league leaders threw three points away on their return from the mid-season break on Tuesday as Inter came from behind to earn a 1-1 draw.
Carlos Tevez fired Juve in front after five minutes but they were unable to hold onto the win as Mauro Icardi secured a point, much to the frustration of Allegri.
Juve travel to Naples on Sunday to meet Napoli, and the head coach knows his side must switch back on if they want to remain top of the table.
"On Tuesday we had the win in our grasp but made four individual errors against a strong side," he said.
"Winning in Naples is never easy but we've got all the required quality to go there and get three points. We must keep a clean sheet tomorrow and win the game.
"Serie A isn't won with 10 or five games to spare. It will be a closely fought season right until the end."
Allegri also hinted at arrivals at the Juventus Stadium during the transfer window, but insisted he only make additions if they can strengthen his squad.
"Top rate players are required to bolster this squad, although it's difficult to get them in January," he added.
"We won't bring players in just for the sake of it, there's no use in that. They have to be the right fit."
