Barcelona - Australian Daniel Ricciardo was fastest on the first day of pre-season Formula One testing in Barcelona on Monday.
The Red Bull driver was the only one to complete more than 100 laps and set a fastest time of 1min 20.179sec around the Catalunya circuit.
Finn Valtteri Bottas of Mercedes was second at 0.170sec with his compatriot Kimi Raikkonen at 0.327 in a Ferrari.
The four fastest times were all set in the morning session as deteriorating weather in the afternoon, including rain, affected the drivers.
Twice former world champion Fernando Alonso had a difficult day, ending in the barriers after the right rear wheel on his McLaren came off.
However, the Spaniard was still able to set the fifth fastest time, behind Renault's Nico Hulkenberg in fourth.
Britain's world champion Lewis Hamilton only completed 25 laps and finished with the seventh fastest lap.
Meanwhile, Toro Rosso rolled out their new Honda-powered 2018 car before pre-season testing got underway.
"I am convinced Honda has the capacity and the know-how to develop the engine to a level that we will be there, where we expect to be," said team principal Franz Tost on Toro Rosso's switch from a Renault engine.
Honda has had problems with reliability and poor performance since its return to F1 in 2015 following a 10-year absence.
A two-year partnership with McLaren proved fruitless while last year Sauber cancelled plans to take Honda engines this season.
"Honda have made a lot of progress in the last months on the reliability side as well as the performance side, so we are looking forward to the season," insisted Tost.
New Zealander Brendon Hartley set the eighth fastest time for Toro-Rosso, less than five hundredths of a second slower than Hamilton.
1. Daniel Ricciardo (AUS/Red Bull-Renault) 1:20.179 (102 laps)
2. Valtteri Bottas (FIN/Mercedes) 1:20.349 (58)
3. Kimi Raikkonen (FIN/Ferrari) 1:20.506 (80)
4. Nico Hulkenberg (GER/Renault) 1:20.547 (73)
5. Fernando Alonso (ESP/McLaren-Renault) 1:21.339 (48)
6. Carlos Sainz Jr (ESP/Renault) 1:22.168 (26)
7. Lewis Hamilton (GBR/Mercedes) 1:22.327 (25)
8. Brendon Hartley (NZL/Toro Rosso-Honda) 1:22.371 (93)
9. Lance Stroll (CAN/Williams-Mercedes) 1:22.452 (46)
10. Romain Grosjean (FRA/Haas-Ferrari) 1:22.578 (55)
11. Marcus Ericsson (SWE/Sauber-Ferrari) 1:23.408 (63)
12. Nikita Mazepin (RUS/Force India-Mercedes) 1:25.628 (22)
13. Sergey Sirotkin (RUS/Williams-Mercedes) 1:44.148 (27)