Hamilton's team switch from Mercedes to Ferrari was a bombshell when it became a fact in February last year – barely a year before the switch would take place.
The seven-time World Champion didn't do better than seventh in the World Championship series last year, his last year in Mercedes.
Instead, he had to see Max Verstappen, the Netherlands, take his fourth consecutive World Championship win with Red Bull.
Lewis Hamilton's enthusiasm on Thursday was not dampened by being beaten by the driver he replaces in Ferrari, Carlos Sainz Jr.
The Spaniard, who drives for Williams, made the fastest lap and was 31 thousandths of a second faster. Both were a second faster than on Wednesday.
Hamilton's teammate Charles Leclerc was third fastest.
The final test day in Bahrain is on Friday. The F1 premiere is held in Melbourne on March 16.
