Little-known Spike Goddard from Sydney went quicker than Daniel Ricciardo in his Formula One test overnight and tweeted "WHAT A CAR!!!" of the Force India VJM07 he drove.
Goddard, 22 – who finished 23rd in this year's European Formula Three Championship in his fourth season racing internationally – completed 89 laps, or 494km, around Abu Dhabi's Yas Marina grand prix circuit.
He was sixth fastest of the 11 drivers on the track on the second and final day of F1's official post-season test.
Ricciardo was seventh fastest but Red Bull packed up a couple of hours early after a mechanical failure on his RB10 caused him to stop out on the circuit.
German 20-year-old Pascal Wehrlein ended the test fastest for the Mercedes factory team in the W05 model car in which Lewis Hamilton won the world championship on Sunday and in which his teammate Nico Rosberg was the season's runner-up.
An interim McLaren car powered by that team's returning engine supplier Honda was plagued with teething troubles at the Abu Dhabi test. Belgian test driver Stoffel Vandoorne could do only five laps in the McLaren over the two days.
Goddard did more than 1.5 times a GP distance in his day in the Force India car – more than twice the distance GP2 series champion Jolyon Palmer drove the day before when the VJM07's running was restricted by issues with its Mercedes engine.
Goddard's fastest lap, 1 minute 44.944 seconds, also was better than Palmer's best, 1:45.516, although the Wednesday times generally were quicker than Tuesday's and the Englishman, son of ex-F1 racer Dr Jonathan Palmer, had been fourth fastest of the 10 drivers to test on the first day.
The official F1 website listed Ricciardo's best lap on Wednesday at 1:45.151 but Red Bull Racing said it was only 1:46.078.
The 25-year-old West Australian, third in this year's world championship after winning three GPs, clocked the fastest lap in Sunday night's season-ending GP on the same circuit – 1:44.496.
However, none of the times in that race or the subsequent testing have come anywhere near Rosberg's pole position lap last Saturday of 1:40.480.
Goddard, who is thought to have paid a substantial fee to drive the Force India for a day, (see our earlier report)was just excited to get his chance in an F1 car. He tweeted the night before: "Struggling to get to sleep, tomorrow I drive a formula 1 car!!! So excited, one of my dreams coming true."
Early on Wednesday he tweeted: "Today's the day!!!!"
And, after having driven the car, he reported that he "was able to have a few laps towards the end to push on. WHAT A CAR!!!"
In a post-test release from Force India he added: ""I felt today went really well.
"The VJM07 is a massive step up from my F3 car, so the first part of the day was devoted to adjusting to the new machinery.
"The power and downforce of these cars is something on a completely different level; it was a massive shock to the system, but I got used to it fairly soon.
"We chipped away at the lap time in every run and in the end we got to a pretty good time and 89 laps, which is a fair bit of running.
"I am pretty happy about the work I did with the team and the way everyone worked with me. I'd love to keep a link with Sahara Force India: it's a fantastic group of people and I'd like to contribute and help as much as I can."
Force India's chief engineer Tom McCullough said: "Spike did a good job and really made the most of his first opportunity in an F1 car. It's always a big jump from F3 to F1, but he adapted quickly and gradually built up his confidence and speed."
Ricciardo drove 87 laps and said the day had been "pretty good", despite the early finish for Red Bull.
"Obviously we got cut short by a couple of hours and it would have been nice to finish the session, but we did a lot of laps and all of those were productive," Ricciardo said.
"There was a little bit of work with this year's tyres and a bit with next year's, trying to understand how those behave.
"We also did quite a few things on starts, trying to understand what's happening there, which was positive.
"I felt pretty good in the car. It's a good way to end the season, we achieved a lot. Now that's it, a bit of time off and look forward to next season."
Ferrari protege and GP2 race winner Raffaele Marciello was second fastest on his F1 testing debut with the Italian team, and 17-year-old Dutchman Jos Verstappen – who will race in Melbourne's season-opening GP next March – third for Red Bull's junior team Toro Rosso.
The Honda-powered McLaren did just two laps after three on the first day.
An electrical issue was discovered as the car was about to head out in the morning and it was only in the final hour that it emerged from the garage but Vandoorne soon stopped out on the track.
"Although this looked like another difficult day, this is just part of the learning experience we expected when we took on the interim car program," McLaren racing director Eric Boullier said.
"I'd rather be ironing out these problems here in Abu Dhabi than discovering them in Jerez [in Spain] next February."