Fernando Alonso finally brought Brawn GP's run of P1 finishes to an end at Jerez on Monday.
This week's test marks the final outing for the teams before the new in-season testing ban is triggered as they head to Australia, making each lap vitally important to the four teams present.
Alonso, in something of a surprise, proved to have the better pace on Monday as he put in a late charge to clock a 1:18.343 that brought the Brawn GP team's run of top-placed finishes to an end.
Brawn GP, formerly Honda, weren't far behind the Renault, with Rubens Barrichello claiming second place with the 1:18.398 that he set during the morning session before handing over to team-mate Jenson Button in the afternoon.
Button continued Brawn GP's impressive run of form, setting the third place time, just under half a second off Barrichello's pace.
Lewis Hamilton, who got behind the wheel for the first time today after missing out on Sunday's action reportedly because the team didn't have the parts needed for the MP4-24, claimed fourth place despite a trip across the gravel. McLaren, though, still have plenty of cause for concern as the reigning World Champion was over a second off the pace.
Nico Rosberg, who replaced Nico Hulkenberg for day two's running, completed the timesheets in fifth place. The Williams driver, though, was the busiest man on track, completing 123 laps.
01. Alonso Renault 1:18.343 99 laps
02. Barrichello Brawn GP 1:18.398 62 laps
03. Button Brawn GP 1:18.892 12 laps
04. Hamilton McLaren 1:19.513 85 laps
05. Rosberg Williams 1:19.783 123 laps
Source : Planet F1