German teenager Sebastian Vettel showed he was ready to come of age in Formula One on Friday by shining in free practice for his race debut in Sunday's US Grand Prix.

A test and reserve driver for BMW Sauber, the 19-year-old was drafted in to replace Robert Kubica at Indianapolis after the Pole failed a medical following his horrific crash in Canada [Images] last weekend.

Vettel, who last August became the youngest driver to take part in a Formula One weekend when he carried out Friday practice duties in Turkey, showed he deserved the chance with consistently quick times in the morning.

In the opening session, he was fourth fastest behind McLaren's double world champion Fernando Alonso [Images], his BMW team mate Nick Heidfeld and F1's brightest new prospect and championship leader Lewis Hamilton [Images].

Vettel was unable to match that in the afternoon, recording the 11th best effort, but was pleased overall with his first run at the Brickyard and first outing in a Formula One car since Malaysia in April.

"Of course it is completely new task for me but so far I am quite happy with what I did," said Vettel. "I thought the track was quite good with a nice rhythm and it's quite interesting to drive with with the banking.

"After a couple of times you get quite used to it and it's fun."

The German, who will be 20 on July 3, will be the youngest in Sunday's race and one of the youngest to start a grand prix since the world championship started in 1950.

Only five other drivers have made their race debuts at the age of 19, including double world champion Fernando Alonso with Minardi in 2001.

Vettel faces a steep learning curve but was given as many laps as possible on Friday to help with his education.

"Sebastian did a good job," said BMW technical director Willy Rampf. "For him we extended the usual programme in order to give him more time to learn the track.

"He did 83 laps which means he did more than anyone else."

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