Romain Grosjean announced Lotus's return to pre-season action by setting the pace as the final test of the winter got underway.
Romain Grosjean moves ahead of Jenson Button late on day one
Romain Grosjean announced Lotus's return to the pre-season testing scene in dramatic style by vaulting to the top of the timesheet in closing stages of the first day of the final test.
The Enstone-based outfit suffered a major setback in their preparations for the new season at the start of last week's test at the Circuit de Catalunya when the discovery of a fault with the new second E20 chassis led to the team aborting the whole test while they worked to remedy the problem.
But with the front suspension issue now fixed, the team returned to action on Thursday and with just under half an hour in the day to go Grosjean vaulted past long-time pacesetter Jenson Button to the top of the timesheet with a lap of 1:23.252 at the start of a short four lap-run on the soft tyres.
Up until then it had seemed destined that McLaren's MP4-27 would finish on top of the pile for the first time this winter after Button usurped early pacesetter Sergio Perez in the final hour before the lunch break.
Having not been seen much on track at the start of the day while McLaren fitted Melbourne-spec parts to the car, the former world champion's best lap of 1:23.510 came at the start of his own three-lap burst, with initial flying lap followed by a slow-down lap and a subsequent flying lap of 1:23.776.
Sauber's Perez - whose team-mate Kamui Kobayashi set the overall pace here last week - achieved his best lap of 1:23.820 at the start of a four-lap run.
However, rather unhelpfully for everyone but the two teams concerned, Button and Perez's best times were set on a batch of unmarked Pirelli tyres built for contingency purposes in a factory away from the Italian firm's main manufacturing base in Turkey - although the pair's times appear to have been set on the medium compound.
Mark Webber was fifth at lunchtime but ended up in a final spot of fourth, following Grosjean's late intervention, after four laps, three flying, on the medium compound mid-way through the afternoon.
The Australian's previous longer stint had been particularly impressive, however, as only once did he drop out of the 1:28s between first (1:27.993) and last (1:29.041) lap across 16 laps on the hard tyre.
Mercedes again took the honours for the most mileage completed during the day with Nico Rosberg notching up 128 laps on the way to fifth place - the German also lapping in the 1:23s - to put him ahead of Toro Rosso's Jean-Eric Vergne and Force India's Paul di Resta.
Ahead of a big week for Ferrari as they look to begin some serious performance runs with their complex F2012 car, Felipe Massa recorded an unspectacular eighth-fastest time but the team were again carrying out some further developments to the car's exhaust channels which necessitated yet more aero evaluations.
The Brazilian did, however, complete the longest 'long run' of the afternoon as he racked up just under 50 laps including a pit stop.
Meanwhile, Caterham were forced into a last-minute change to their driver schedule after Heikki Kovalainen fell ill overnight, Vitaly Petrov instead commencing their work at the final test.
The Russian, after a problematic first week in the CT01, got a mammoth 123 laps under his belt this time including a solid afternoon long run - his best time from the morning having been just 1.6 seconds off the ultimate pace.
He did stop on track right at the end of the day to bring out the red flag, although this is likely to have been a dry fuel run.
Williams, meanwhile, circled at the back all day with last week's second-fastest man Pastor Maldonado with the Grove squad concentrating primarily on high-fuel runs across his 58 laps.
Day one times:1) Grosjean 1:23.252 73 laps
2) Button 1:23.510 64
3) Perez 1:23.820 118
4) Webber 1:23.830 102
5) Rosberg 1:23.992 128
6) Vergne 1:24.216 113
7) Di Resta 1:24.305 98
8) Massa 1:24.318 105
9) Petrov 1:24.876 123
10) Maldonado 1:25.587 58
