Aguero shot to equal-top of the golden boot standings with nine - level with Chelsea hit-man Diego Costa - after scoring two goals from free play and two penalties at the Etihad.
The 26-year-old overtook former City front man and compatriot Carlos Tevez as the record-holder of the most Premier League goals for the club, with 61 in 95 appearances.
And Hart said Aguero's brilliance was all the more stunning given his supposed lack of touch on the training track.
"He is one of those players and I don't think he will be unhappy with me saying it, that some days you look at him in training and he is useless," England international Hart said.
"But you know that when it comes to games he is going to score, because he is that talented, that good a player. He is a big-game player."
Aguero could have had even more goals to his name against Spurs, missing opportunities including a 32nd-minute spot-kick.
Hart said his team-mate should be lauded for not dropping his head after missed chances.
"Sergio deserves all the plaudits he gets," he said. "He has scored four goals and he will be miffed at missing other chances.
"But he kept plugging away when anyone else might have let missing the second penalty put them off. He showed his quality.
"The two penalties he scored were nice but the other two finishes were fantastic - and they were required because [Tottenham goalkeeper Hugo] Lloris played well."
Hart said Aguero's job was not yet done, despite hailing him as one of the best finishers in the game.
"How good is he? Finishing wise he is one of the best," said Hart. "His goals-to-games ratio in the Premier League is the best.
"But he still has a lot of work to do. He is still only young and hopefully if we keep him fit he will be pushing on.
"He's a very important character in the dressing room and he does all the important things as well as being a brilliant footballer and that's why we're very lucky to have him."
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