Smith has emerged as an impressive influence of late, producing eye-catching displays in Pompey's last two matches.
Hart told The News: "If anybody can tell me that Tommy doesn't look like a Premier League player at the moment, I'd have a big argument with them.
"I think his energy and tenacity have been absolutely fantastic and his performances have been excellent. Obviously, Tommy and Aruna (Dindane) need a goal to propel them into another phase.
"But Tommy has terrific energy, he creates a lot of chances and is doing extremely well. He must be a nightmare to play against.
"I never had any doubts.
"He was a terrific player seven or eight years ago when I first saw him and that hasn't changed. He's doing exactly what I brought him for."