However, it was Scuderia driver Leclerc who made an impressive late charge on C5 Pirelli tyres to continue to drop the time, finishing clear on 1:16.231.
"I think they are really fast, they showed some good pace", he said. "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".
Their new front wing concept has worked wonderfully well for them and they are comfortably ahead of Red Bull and Mercedes at the moment.
"Obviously I think as every team we are not flat-out", he continued.
"I still have to learn", he added, "I get more comfortable with the vehicle lap after lap and with the auto itself, so it's looking good for now".
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Mercedes driver Valtteri Bottas said he felt Ferrari were ahead of the field.
The Italian team did not specify what problem led to Vettel's crash after he ran only 40 laps in the morning session of the second of four days of testing.
A red flag was introduced following the shocking incident while Ferrari later confirmed a "mechanical problem" was the cause of the accident.
Given the extent of the damage to the vehicle, he might not be appearing until much later in the day. The vehicle instantly bottomed out and went straight into the Tecpro barrier on the outside of the circuit, causing a 40-minute delay while the auto was removed and barrier fixed. The most important thing is we can get Max (Verstappen) in the vehicle tomorrow.
Friday will be the last of the eight days of pre-season testing.
"I'm quite happy with how winter testing went as I was able to do a lot of laps and maximize my time in the auto", the rookie said. Given that both cars had race fuel loads, used the C2 compound over three stints and started within 30 minutes of each other, the coinciding race sims are arguably the closest thing we have seen to a true comparison in testing so far.
The season-opening Australian Grand Prix is on March 17.