David Coulthard broke the Valencia lap record on Thursday on only the third day of testing for McLaren's new car.
The Scot was fastest of all at the Spanish track, clocking one minute 10.021 seconds in the car he will be driving in the 2004 Formula One season.
Coulthard was keen to point out that winter test times can be deceptive.
"Is it quick enough to win a Grand Prix? We just won't know until we get to Melbourne and see what everyone else can do," Coulthard said.
Coulthard was 0.2secs quicker than Juan Pablo Montoya, who was next fastest in a 2003 Williams.
F1 testing times are notoriously unreliable indicators of form as it is difficult to accurately assess the condition of the car, the amount of fuel it is carrying and the tyres used.
However, it is still hugely impressive for a new car to achieve such quick times so soon.
The MP4-19 is a development of the MP4-18 which was intended to race last season until a series of faults and setbacks meant McLaren had to use a modified version of their 2002 machine.
Valencia test times:
1 David Coulthard (GB) McLaren MP4-19 1:10.021
2 Juan Pablo Montoya (Col) Williams 1:10.218
3 Jarno Trulli (Ita) Renault 1:10.419
4 Ralf Schumacher (Ger) Williams 1:10.601
5 Marc Gene (Spa) Williams 1:11.013
6 Franck Montagny (Fra) Renault 1:11.035
7 Alexander Wurz (Aut) McLaren MP4-17D 1:11.252
8 Ryan Briscoe (Aus) Toyota 1:11.562
9 Justin Wilson (GB) Jaguar 1:11.866
10 Mark Webber (Aus) Jaguar 1:12.133