Jenson Button

THE ASSOCIATED PRESS

VALENCIA, Spain -- Defending Formula One champion Jenson Button had a "useful" first day with McLaren despite being frustrated it took so long to adjust the seat of his car.

The Briton was fifth fastest in Wednesday's test session, finishing nearly 1{ seconds back of pace-setter Fernando Alonso of Ferrari at the season's opening testing session.

Button said the day was about getting used to his car and he eventually "got to grips" with it after the early difficulty.

"It was a useful day but it was a little bit frustrating this morning it took us a long time to sort the seat, but that's how it is the first time with a new team," said Button, who wouldn't compare his new car to Brawn GP's last season that took him to his first title.

"It would have been nice to have got some more testing done, set-up work. But this test was always to get used to environment inside the cockpit, get used to the team and to run through all of the checks you do at the first test."

Button found himself high and uncomfortable in the cockpit, but eventually fixed the problem before driving 82 laps.

"It's very difficult because this is not the best circuit to get a feeling for how the car is going to be at the start of the season," Button said. "Today has been a busy day of finding my way around the cockpit."

Button is looking forward to racing on a grid that will have three other F1 champions -- Hamilton, Alonso and Michael Schumacher, his replacement at Brawn that is now named Mercedes GP.

Ferrari was fastest in each of the three sessions, but Button was wary of taking too much notice.

"Ferrari are fast but we don't know how fast. You never know what fuel they are running when they do those times," Button said. "This is the wrong place for us to be thinking about who's fast and who isn't."

Being the defending champ, Button has earned the No. 1 sticker on his car this season.

"It's always nice walking into the garage and seeing your name on the car and No. 1," Button said. "But when you get down to business and close your visor you don't think about the number on the car."