When the new Nurburgring GP-Strecke—the same basic F1 circuit we see in use today—opened in 1984, Mercedes bosses organised an exhibition race to celebrate. Twenty of the world's finest drivers took part, each driving a Mercedes 190E saloon.
The field was impressive and included future and former world champions—including Niki Lauda, Alain Prost, Denny Hulme, James Hunt, Alan Jones, Jack Brabham and Keke Rosberg.
Emerson Fittipaldi was due to take part but was busy with the Indy 500, so Senna was recruited to take his place. At the time, he only had three F1 starts and two points under his belt.
Prost, who gave Senna a lift from the airport, told a Top Gear DVD about the day (h/t ESPN):
We had a 10- or 15-minute time difference [in flights] and I had a car, so I was waiting to take him to the Nurburgring. That was the first time we talked together and we had a long drive, something like two or three hours, so we had time to talk.
He didn't talk very much but he looked impressed because I was driving very fast on the motorway in Germany and he said: 'You know you're driving fast!' It was nice and we were quite close because he didn't know anybody, so he was always close to me during the first days.
It was very funny because he looked very open, very nice and then we started the practice and we were fighting together for pole position. I saw him being very competitive; I took the pole, he was second and then at the start he went before the flag and I said to myself 's---, I have to take care of this guy!'
In damp conditions, Senna barged past Prost on the opening lap and went on to win the race.
It wasn't the fact he won that was impressive, rather it was the manner he went about it. To Senna this wasn't a fun exhibition race—it was just a race like any other, and he had to win.
Afterwards, per Top Gear, Senna said: "Now I know I can do it."
Everyone present did too.