Leclerc's best lap in 1m16.231s on the softer C5 complex proved that 2019 F1 cars are faster than last year.
The lap was almost a second faster than Sebastian Vettel's best effort of last year, when he achieved the best overall time of 1m17.182.
Despite confirming Ferrari's place as a pre-season favorite, Leclerc said he felt that there was even more performance that could be unlocked from the SF90.
"Obviously, like all teams, we are not up to the task," he said. "There is still a margin, there is a little in me, I still have to learn.
"I'm more comfortable with the car after lap, and also with the car itself, so it looks good at the moment."
Leclerc said his positive feeling within the Ferrari has not changed since the first encouraging race of last week.
"The car is comfortable, the scale is pretty good from the first day and it has not changed today," he said.
"It's a positive day, especially after the lack of racing yesterday.It was a good morning for us and it's good for us to be on top, but that's okay." say."
His rival, Mercedes, believes that he is still behind Ferrari, but Leclerc refused to take anything for granted about the opposition's position.
"It's hard to repeat, it's a test," he said. "We seem strong right now, but they know more or less well, we do not know it and we will only know it in qualifying.
"For now, we are quite satisfied with the work we do."
When asked if, with his own money, he would bet on Ferrari for Australia, Leclerc replied: "For now, I'm happy, so yes."