Pastor Maldonado was the surprise package on day three in Barcelona as he set the pace during the morning session.
After Force India's Nico Hulkenberg and Sauber's Sergio Perez claimed the top two positions on day two, it was the Williams driver's turn to take top spot on the penultimate day.
The Venezuelan posted a 1:22.391 - the fastest time of the week so far - on super softs shortly before the lunch break. His time was almost a full second faster than that of second-placed man Michael Schumacher, who set the pace much earlier in the day.
Kamui Kobayashi followed up team-mate Perez's good work on Wednesday with a 1:23.582 which was good enough for P3 while McLaren's Jenson Button was 0.368s off his pace in fourth place.
Ferrari's Felipe Massa, who did some straightline aero runs, was down in sixth place with Mark Webber from Red Bull in seventh. Massa spent quite a lengthy period in the garage with a mechanical problem, but he was able to return to the track before lunch.
Red Bull, meanwhile, once again focused on pit stops and full race simulations and Webber completed only 26 laps. That, though, was still six laps more than what Paul di Resta managed to do in the morning after his VJM05 lost a part of his engine cover.
Vitaly Petrov also had a frustrating morning as "front suspension issue" saw him complete just 23 laps.
Unofficial times
1. P Maldonado Williams 1:22.391 52 laps
2. M Schumacher Mercedes 1:23.384 +0.993 54
3. K Kobayashi Sauber 1:23.582 +0.970 59
4. J Button McLaren 1:23.918 +1.527 39
5. J Vergne Toro Rosso 1:24.433s +2.042 42
6. F Massa Ferrari 1:24.771 +2.380 48
7. M Webber Red Bull 1:24.835 +2.444 26
8. T Glock Marussia 1:26.173 +3.782 51
9. V Petrov Caterham 1:26.929 +4.538 23
10. P Di Resta Force India 1:27.180 +4.789 20 laps
