Brendon Hartley admitted it had been a dream come true to take part in his first F1 test proper during the first day of running at Jerez.
The Kiwi, who finished third in the British F3 International Series standings in 2008, was given the chance to test the RB4 in Spain following Mark Webber's cycling accident, which left the Australian out of action until the New Year.
Although he has previously completed straight line tests for both Red Bull and Toro Rosso in the past, the Jerez test marker Hartley's first true experience of Formula One machinery and he enjoyed a trouble-free day at the wheel – with his only issue coming at the end of his first lap when he missed the entry to the pit-lane.
That aside, Hartley produced an encouraging performance to end the day third quickest, just two-tenths of a second behind the BMW Sauber of Nick Heidfeld.
"This has been an amazing experience," Hartley admitted. "The first run was really difficult, just in terms of the mind speeding up, as everything's going so much faster than normal.
"There's a lot of things to think about with button's and radio calls, but I got more and more confident with the car and it was going well by the end of the day. It's a dream come true really. I've been working for this all my life and it's been unbelievable."