BARCELONA (Reuters) - Formula One fired up its final four-day pre-season test on Tuesday with champions Mercedes trying out new aerodynamic parts and Italian Antonio Giovinazzi fastest for Alfa Romeo.
Giovinazzi's best lap of one minute 18.589 seconds in the Ferrari-powered car was set using the second softest C4 compound tyres towards the end of a sunny session at the Circuit de Catalunya outside Barcelona.
Red Bull's Pierre Gasly was second on the timesheets with Ferrari's new recruit Charles Leclerc third, both on harder rubber.
Leclerc managed only 29 laps with the Monegasque losing track time as Ferrari checked the car's cooling system.
Five times world champion Lewis Hamilton was eighth quickest of the 10 drivers on track but did 83 laps, the second most and one less than Haas driver Kevin Magnussen. Both were on the second hardest C2 tyres.
The Briton, focusing on long runs, had a different front wing to the one used last week.
Williams had a more encouraging morning, after missing most of the first test due to the late build of the car, with British rookie George Russell doing 46 laps -- more than he managed last week -- with the sixth fastest time.
McLaren's Lando Norris brought out red flags when he pulled over halfway through the session with 38 laps done and the team's former driver Fernando Alonso arriving in the paddock to watch the afternoon running.
The season starts in Australia on March 17.
(Writing by Alan Baldwin in London, editing by Alexander Smith)