Pastor Maldonado topped the timesheets on the third day of pre-season testing at the Circuit de Catalunya.
The Venezuelan's lap of 1.22.391 was almost a second clear of his nearest rival in Barcelona.
Michael Schumacher completed a race simulation in the afternoon, taking his lap total to 127 - encouraging for Mercedes after gearbox problems on Wednesday.
A few red flags interrupted the day's running as Mark Webber, Felipe Massa and Kamui Kobayashi all stopped on track, while Paul di Resta lost an engine cover in the morning.
Vitaly Petrov caused a brief flutter when he went first with the fastest time of the week, although there was a glitch with the timing system, which knocked five seconds from his lap time.
The test concludes tomorrow.
1 | Maldonado | Williams | 1m22.391s | 106 |
2 | Schumacher | Mercedes | 1m23.384s +0.993 | 127 |
3 | Kobayashi | Sauber | 1m23.582s +1.191 | 99 |
4 | Button | McLaren | 1m23.918s +1.527 | 114 |
5 | Vergne | Toro Rosso | 1m24.433s +2.042 | 78 |
6 | Webber | Red Bull | 1m24.771s +2.380 | 97 |
7 | Massa | Ferrari | 1m24.771s +2.380 | 84 |
8 | Di Resta | Force India | 1m25.646s +3.255 | 83 |
9 | Glock | Marussia | 1m26.173s +3.782 | 108 |
10 | Petrov | Caterham | 1m26.448s +4.057 | 70 |