Rain ahead of, and during, the opening 90 minutes of track time at the Japanese Grand Prix saw Formula One's ten teams take differing approaches to free practice, with Heikki Kovalainen eventually topping the timesheets.
Despite being a newcomer to the venue, the Finn posted a target time of 1min 40.356secs in the course of 24 laps to keep local favourite Kazuki Nakajima off top spot as the Suzuka circuit failed to dry sufficiently to allow for slick tyre running.
Both McLarens looked quick early in the session, which began wet and got wetter before the conditions abated and allowed for greater improvements later on. Team-mate Lewis Hamilton succeeded Kovalainen at the top, before Sebastian Vettel stuck in a lap nearly a second faster than anyone else mid-session. Such were the changing conditions, however, the German ended the morning down in 17th spot after completing just eleven laps due to concerns over both his engine and tyre supply ahead of a crucial weekend for his title ambitions.
Hamilton returned to the top of the list for a short time, before Nakajima replaced him. The under-fire Williams driver appeared to have cemented P1 with further improvement that returned him to the head of an ever-changing order, only for Kovalainen to usurp him as the chequered flag appeared.
Fernando Alonso, Adrian Sutil and Sebastian Buemi all also took turns at the top of the pile, with Sutil and Buemi both remaining in the top five at the end, taking third and fifth spots and sandwiching Giancarlo Fisichella, who vaulted up the order with his own late lap. Alonso wound up seventh fastest, one spot beind Hamilton, with Kimi Raikkonen, Rubens Barrichello and Nico Rosberg completing the top ten.
Championship leader Jenson Button was only 18th fastest, some 2.9secs off the pace, but appeared unconcerned as the conditions made final placings something of a lottery. The Briton completed just 17 laps of a circuit he knows well, and will look to stake his claim if the surface dries out in time for second practice. Fisichella, still learning the nuances of Ferrari's F60, and Toro Rosso rookie Jaime Alguersuari completed the greatest number of laps, with 27, while Red Bull's Mark Webber - like team-mate Vettel, concerned about his dwindling engine supply - put in just ten laps.
Missing from action was Toyota's Timo Glock, the German replaced by team reserve Kamui Kobayashi after being advised to rest as the effects of a fever took their toll. Toyota insists that it will re-evalaute Glock's situation when it comes to day two, but cynics believe that Japanese newcomer Kobayashi will remain in the cockpit for the remainder of the weekend. The reigning GP2 Asia Series champion ended the morning 19th fastest, ahead only of former rival Romain Grosjean.