Toro Rosso driver Alexander Albon of Thailand topped the timesheets on Thursday's early sessions. AP Photo / Manu Fernandez.

Barcelona - Thai racer Alexander Albon kept Toro Rosso on top of the Formula One testing timesheets at lunchtime on Thursday while Mercedes unlocked a little more pace and finally went faster than Ferrari.

British-born Albon, one of three Formula Two graduates making their F1 race debuts when the season starts in Australia on March 17, lapped the Circuit de Catalunya with a best time of one minute 17.637 seconds on the softest and fastest tyres.

He also completed another 44 laps after an impressive 132 on Tuesday, with the Honda engine showing good gains in both performance and reliability after the problems of recent years.

Albon's Russian team-mate Daniil Kvyat had produced the fastest lap on Wednesday, a 1:17.704 but also on softest of tyre compounds.

Australian Daniel Ricciardo slotted in with the second fastest time for Renault, a 1:17.785 also on the softest tyres on a cold but sunny morning.

Five-times world champion Lewis Hamilton was third for Mercedes, which had said on Wednesday that it planned to focus a bit more on performance, and just under the 1:18 barrier with a 1:17.977 on harder tyres than the top two.

Ferrari's Charles Leclerc was fourth on the timesheets in 1:18.046, but on a harder compound than Hamilton.

The Monegasque did the most laps, however - his 75 before lunch comparing to Hamilton's 58. Frenchman Romain Grosjean did 64 in the Ferrari-powered Haas.

Poland's Robert Kubica was also on track for Williams, who only started testing on Wednesday afternoon, and did 48 laps. He was still 10th and slowest, more than a second and a half off Canadian Lance Stroll for Racing Point.