Leclerc, who joins Ferrari in only his second season in Formula 1 after a stellar debut for the affiliated Sauber team in 2018, said he was happy with his team's progress after recording a time of one minute 16.231 seconds.
Leclerc set the fastest time of the winter by more than half a second before Gasly damaged the Red Bull at the high-speed Turn Nine, his second crash this winter.
He later stopped on track with an exhaust issue but the overall tone emanating from the team was upbeat. "We have some potential, we tested a lot of things, we have good performance, but we have to work hard as well as they seem really fast".
The season starts in Australia on March 17.
"The vehicle feels comfortable", he admitted, "from day one the balance is pretty nice and it hasn't changed today, so it's a positive day".
While Red Bull have impressed with their new Honda engine, Gasly said Ferrari were still ahead. To be fair, I think they are really fast, they show some good pace, try to focus on ourselves and not focus too much on the others.
"The whole field looks like it's a bit tighter than last year or the year before, but it's only guessing", added the Finn.
McLaren rookie Lando Norris also impressed as the 19-year-old twice set another fastest time, moving clear again of Toro Rosso's Alex Albon at 1:17.084.
Norris's team mate Carlos Sainz, who went quickest on Wednesday, played down the times.
World champion Lewis Hamilton set the 10th fastest time - an impressive 1:18.097 on the second hardest tyre, while almost everyone else set their best laps on the softest rubber.
Bottas did 96 laps after lunch but his best effort of 1:18.862 was still the slowest time of the day. He had completed 138 laps - two race distances - by that stage.