Felipe Massa set the pace for Williams on the first day of Formula 1's final pre-season test at Barcelona as McLaren and Mercedes were hampered by mechanical issues.
Massa bolted on a set of soft tyres and completed a three-lap qualifying simulation run in the afternoon, clocking a 1m23.500s.
It's the fastest time set in Barcelona testing so far, with the Brazilian eclipsing Lotus's Romain Grosjean's leading time from the last test by just over four tenths.
A late run on the supersoft tyres moved Sauber's Marcus Ericsson up to second quickest with Lewis Hamilton, who set the pace in the morning session on the medium tyres, third.
However, Mercedes' Hamilton did not complete a single lap after lunch following a failure with the MGU-K that the team could not fix in time to get the car back out on track.
McLaren's afternoon was also curtailed with a hydraulics issue, meaning Jenson Button managed just seven laps, of which only one was timed.
Ericsson completed a race simulation in the afternoon, using the medium and hard tyres, and clocked 122 laps - the highest tally of the day.
Red Bull's Daniil Kvyat, who brought the day's first red flag when he stopped at the pit exit in the morning, only did 30 laps in the afternoon.
That brought the Russian's tally to 75, as he finished fourth fastest, 2.4s off the pace.
Carlos Sainz Jr stopped at Turn 10 in the afternoon, bringing out the red flag for the second time.
The Toro Rosso driver completed 86 laps and ended up seventh, just ahead of Button who propped up the timing screens.
Elsewhere, Grosjean completed 75 laps and Ferrari's Kimi Raikkonen 80 as they finished fifth and sixth respectively.
DAY ONE TIMES
|4||Daniil Kvyat||Red Bull/Renault||1m25.947s||2.447s||75|
|7||Carlos Sainz Jr.||Toro Rosso/Renault||1m26.962s||3.462s||86|