Nico Rosberg put in the test lap equivalent of driving from Silverstone to Spa on Thursday to dispel any doubts about the new Mercedes Formula One car that he and Lewis Hamilton will be racing this season.
After two troubled days, with Rosberg able to complete only 14 laps on Tuesday and 2008 champion Hamilton doing just 15 before crashing on Wednesday, Mercedes made a show of their reliability.
The W04 car ran like a train all day, with the German driver completing 148 laps of the Jerez test track with barely a break for lunch.
By the close, he was second on the timesheets with comfortably the most laps covered.
Hamilton, who is back in the car on Friday for the final day of the season's first test, will be happy to hear it after a brake failure at 260kph sent him piling into the tyre wall on his first outing with the team.
Rosberg, winner in China last year with a car that was otherwise uncompetitive for most of the year, was delighted with the 24 hour turnaround.
"I've never been as well prepared for a season as this year because I remember in previous years I've always been a bit tired, but today no problem," he told reporters. "I have a few pains here and there, but I'm really on top form, and so I'm very pleased.
"The last two days we were just massively unlucky because we had problems that were small things and we were not able to solve them in a day," he added. "But today really made up for it. It was fantastic and it really put a smile on everybody's face."
The total distance covered of 655km was more than two race distances and beat the highest single-day total of 132 laps from last year's test set by now-retired seven-times champion Michael Schumacher.
It was also roughly the same distance as that by road between the British Grand Prix circuit and Spa-Francorchamps in Belgium - a feat that was not lost on Rosberg, who rounded off his afternoon with some pitstop practice.
"It's a fantastic achievement to drive from Silverstone to Spa, distance-wise, in one test day with the F1 car with no problems whatsoever, pounding out the laps, being very consistent," he said.
"Today showed we have a very reliable car. Nothing at all went wrong, not the slightest thing."