Mark Webber set a blistering pace on Friday where, thanks to a day of sunshine, he posted this year's fastest lap time at the Jerez circuit.
After finishing top of the timesheets with a lap of 1:19.299, the Aussie reported: "We're certainly showing some good form in terms of reliability, but we always need to work on performance - you never know what the other teams are doing.
"But we're in a good position at the moment to build up to the first race.
"It's close, but there's also quite a way to go, as other teams have no doubt planned developments for Bahrain.
"We're doing the work we need to do in order to understand the car more."
Report: After two days of rain and interruptions, Friday's running at the Spanish circuit kicked off under blue skies and with the track almost completely dry.
However, even the dry surface didn't stop the red flags from being waved as the action was halted on six occasions.
Heikki Kovalainen brought out the first red flag in the opening hour when the Lotus driver came to halt at Turn 9 with the team reporting that the "car stopped with a clutch sensor failure."
Lotus, though, were the only newcomers to run into problems as Virgin Racing, having a great start to the day, soon found themselves beached in the gravel.
Lucas di Grassi, who took over from team-mate Timo Glock for the final two days of testing, put in a respectable 1:31.6, which had the team crowing about that great "Friday feeling!" Five minutes later, di Grassi's VR01 was in the gravel and the red flags were once again being waved.
No soon had the action started than it stopped again, this time it was Kamui Kobayashi, who came to a halt out on track on his very first lap out of the pits.
"A festival of red flags so far," is how Ferrari described the first few hours of testing.
And hour of clear running on an ever-drying track followed, allowing Jenson Button, Mark Webber and Fernando Alonso to put in some blistering laps as the trio moved ever closer to last week's leading time of 1:19.583, which was set by Lewis Hamilton.
Their charge, though, came to an end when Webber's RB6 broke down between Turns 8 and 9, red flag number four of the day.
The next stoppage of the day belonged, yet again, to di Grassi, whose VR01 stopped out on track at the Dry Sack hairpin.
There were also additional problems for Lotus with tech boss Mike Gascoyne revealing that a "cracked exhaust pipe" was the cause of Kovalainen's second delay of the day.
With the session once again green-lighted, the drivers continued putting in the laps with six of them hitting the 100 mark.
But while the lap counter climbed, the lap times dropped.
Webber, back on track after his earlier problems, stormed into the lead with a 1:19.4, easily outpacing Ferrari's Alonso.
The Aussie, though, wasn't done and continued to lap, dropping the benchmark time to a 1:19.299, 0.284s quicker than any F1 driver had gone at Jerez this year.
And with the cloud cover building over the circuit, causing the track temperature to drop, Webber's rivals were not able to match the Red Bull racer's pace.
Any chance they may have had with a final dash at the very end of testing was put to rest when Nico Hulkenberg caused the sixth red of the day.
So the day ended with Webber 0.816s ahead of Alonso, Button was third while Hulkenberg, who was the busiest driver with 137 laps to his name, finished in fourth place.
"We have done pit stop practices with the Hulk & race sims. Much better weather-wise today - clear skies = good!" Williams reported.
Seven-time World Champion Michael Schumacher was fifth ahead of Robert Kubica, Adrian Sutil and Kamui Kobayashi. Kobayashi, though, only managed 28 laps as a fuel problem kept him off the track for large parts of the day.
1. M. Webber Red Bull Racing RB6 1:19.299 114 laps
2. F. Alonso Ferrari F10 1:20.115 +0.816 132 laps
3. J. Button McLaren MP4-25 1:20.394 +1.095 101 laps
4. N. Hülkenberg Williams FW32 1:21.432 +2.133 137 laps
5. M. Schumacher Mercedes GP W01 1:21.437 +2.138 79 laps
6. R. Kubica Renault R30 1:21.916 +2.617 100 laps
7. A. Sutil Force India VJM-03 1:21.939 +2.640 69 laps
8. K. Kobayashi Sauber C29 1:22.228 +2.929 28 laps
9. J. Alguersuari Toro Rosso STR5 1:22.704 +3.405 120 laps
10. L. Di Grassi Virgin Racing VR-01 1:23.504 +4.205 34 laps
11. H. Kovalainen Lotus F1 T127 1:23.521 +4.222 68 laps