Kimi Raikkonen of Ferrari led Friday's practice session at the Chinese Grand Prix, with less than two tenths of a second separating the top four drivers.
Two-time defending champion Fernando Alonso of McLaren, was second with Felipe Massa, Raikkonen's Ferrari teammate, third.
McLaren's Lewis Hamilton, looking to clinch the driving championship in his rookie season but with an investigation threatening it, was fourth.
Ferrari and McLaren have won all the 15 races so far with Alonso, Hamilton and Raikkonen all notching up four victories.
There are other free practices Friday afternoon and Saturday morning on the 5.5 kilometer (3.4-mile) Shanghai International circuit. Sunday's race is 56 laps.
Raikkonen's top time was 1 minute, 37.024 seconds. Alonso was at 1:37.108 just ahead of Massa at 1:37.128.
Hamilton was fourth at 1:37.210, nearly a half-second ahead of fifth-place Nico Rosberg of Williams.
Hamilton heads into this weekend's race with 107 points, a 12-point lead over Alonso. Hamilton will become the first rookie to clinch the title if he finishes ahead of Alonso in Shanghai, or maintains at least an 11-point margin with only the Brazilian Grand Prix to go.
However, Hamilton is being investigated by Formula One's governing body for his role in an accident during his victory in last week's Japanese Grand Prix.
FIA said Thursday it was looking into "new evidence" concerning Hamilton's driving behind the safety car in the rain-soaked race at the Fuji Speedway.
Hamilton is said to have speeded up and slowed down, causing Red Bull driver Mark Webber and Toro Rosso's Sebastian Vettel to collide behind him on the 46th lap.
Hamilton was questioned by FIA about the incident Thursday and FIA is expected to announce its decision Friday.
Hamilton could be penalized grid positions in Sunday's race.
Ferrari has won two of the previous three races here and the red cars could be the downfall of Alonso.
If Kimi Raikkonen and Felipe Massa were to finish first and second for Ferrari - and if Alonso and Hamilton follow third and fourth - there would be still be an unassailable 11-point gap Hamilton and Alonso after the race.
Raikkonen, with a slight chance to win the title, is third in the standings with 90 points while Massa has 80.