Force India's Nico Hulkenberg set an impressive pace as the second pre-season test began in Bahrain.
The German posted a 1:36.880 in the afternoon which was quicker than the fastest race lap of the 2013 Grand Prix at the Sakhir circuit.
Hulkenberg's time was a full second clear of the next best car - Fernando Alonso's Ferrari - and the VJM07 also completed a third best 78 laps on the day.
With the exception of Alonso, it was another dominant day for Mercedes powered teams taking three of the top four positions on the timing screens as well as leading the mileage charts with those three teams completing the most laps of anyone with the exception for Adrian Sutil's Sauber.
Mercedes and McLaren completed a somewhat regulatory day completing 74 and 81 laps respectively and finishing third and fourth overall just three tenths apart. Lewis Hamilton was behind the wheel of the W05 with Kevin Magnussen in the MP4-29.
One of the surprises of the day were Williams as Felipe Massa went from topping the timings on the last day in Jerez, to completing just five laps on day one, failing to set a time in the process.
Ferrari's day started off badly with the Spaniard pulling off the track on his first lap after exiting the pits with smoke coming from the back of his F14-T, but it was a mere blip as the rest of the day ran smoothly and Alonso compiled 64 laps, nine more than the regular race distance in Bahrain.
The other Italian powered cars had a mixed first day; Sauber led the lap count with an impressive 82 though Sutil could only achieve 6th fastest while Marussia failed to set a time on Wednesday, Jules Bianchi turning just three laps overall.
The biggest story perhaps from the opening day in the desert was once again the lack of running by the Renault powered cars. Lotus finally gave the public it's first close up of the E22 and it's 'twin-tusk' nose but Romain Grosjean gave it a slow start completing just 8 laps and finishing slowest of the nine teams who set a time.
World champions Red Bull and Toro Rosso were much later than most to emerge from their garages as their issues continued.
Indeed team boss Christian Horner and advisor Helmut Marko were seen deep in discussion with Renault's Rob White as Vettel headed out for the first time around lunchtime.
It emerged that the team were sacrificing performance by cutting holes in the RB10 to allow for extra cooling just in a bid to get some running time but even this didn't help as the German managed just 14 laps, stopping out on track with around 90 minutes to go.
As for Toro Rosso they too caused a red flag on the first day and Daniil Kvyat only achieved five laps throughout the day.
Despite all the troubles of the Mateschitz-backed teams Caterham had quite a successful day. Dutch reserve driver Robin Frijns completed 68 laps, the best daily total of any Renault powered team so far though his 1:42.534 was quite some way off Hulkenberg's fastest time.
Another interesting day with few questions answered and even more created because as the Mercedes and Ferrari powered cars continue to show good reliability at a good pace, it is becoming increasingly clear Red Bull's woes are not completely Renault's fault.
Much of Adrian Newey and co. to contemplate ahead of day two on Thursday.
Bahrain Test, Day 1: Results
1. Nico Hulkenberg Force India-Mercedes 1m36.880s 78
2. Fernando Alonso Ferrari 1m37.879s +0.999s 64
3. Lewis Hamilton Mercedes 1m37.908s +1.028s 74
4. Kevin Magnussen McLaren-Mercedes 1m38.295s +1.415s 81
5. Sebastian Vettel Red Bull-Renault 1m40.224s +3.344s 14
6. Adrian Sutil Sauber-Ferrari 1m40.443s +3.563s 82
7. Robin Frijns Caterham-Renault 1m42.534s +5.654s 68
8. Daniil Kvyat Toro Rosso-Renault 1m44.346s +7.466s 5
9. Romain Grosjean Lotus-Renault 1m44.832s +7.952s 8
10. Felipe Massa Williams-Mercedes no time 5
11. Jules Bianchi Marussia-Ferrari no time 3
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