Barcelona - Williams' Felipe Massa was fastest as McLaren's embryonic relationship with engine supplier Honda suffered another blow on the first day of the third pre-season test in Barcelona on Thursday.
Massa completed more than 100 laps with his best time of 1min 23.500sec, the quickest of the day ahead of Sauber's Marcus Ericsson.
"I think it was a very good day not just because we were in front, but because the car was never in any trouble," said Massa, who ended last season with back-to-back podium finishes.
"I am not sure where we will be in the first race, but until now everything is working well and I am happy about that. The consistency is something we are still working on to improve. It is still early and when everybody is on the same fuel and same tyres at the same time is when we will be sure where we are.
"We need to prove we are there in the fight. We don't know how much with Mercedes, for me they are the strongest team, but I think compared to the others we are there."
Mercedes had their worst day of testing so far, though, as world champion Lewis Hamilton was stranded in the garage for the entirety of the afternoon session due to a MGUK failure after registering the third fastest time of the day early on.
Jenson Button managed just seven laps in the McLaren before lunch as the Woking-based team's struggles for reliability less than a month before the first Grand Prix of the season were again exposed with a hydraulic leak which brought their day to an early end.
With three days of testing remaining, McLaren have managed just 210 laps, well under half of the mileage completed by every other team on the grid bar Force India, who hope to unveil their new JVM08 car for the first time on Friday afternoon.
McLaren chief executive officer Ron Dennis insisted that he expects two-time world champion Fernando Alonso to be fit for the Australian Grand Prix on March 15 despite missing this test after spending three nights in hospital due to a crash in the second test last weekend.
Results from day one of the third pre-season test in Barcelona:
1. Felipe Massa (BRA/Williams) 1:23.500 (103 laps)
2. Marcus Ericsson (SWE/Sauber) 1:24.276 (122 laps)
3. Lewis Hamilton (GBR/Mercedes) 1:24.881 (48 laps)
4. Daniil Kyvat (RUS/Red Bull) 1:25.947 (75 laps)
5. Romain Grosjean (FRA/Lotus) 1:26.177 (75 laps)
6. Kimi Raikkonen (FIN/Ferrari) 1:26.327 (80 laps)
7. Carlos Sainz Junior (ESP/Toro Rosso) 1:26.962 (86 laps)
8. Jenson Button (GBR/McLaren) 1:31.479 (7 laps)