Valtteri Bottas completed a practice clean sweep for the Portuguese Grand Prix.
The Finnish driver, who was quickest in both sessions at Portimao on Friday, held the advantage over Lewis Hamilton with the world champion trailing his Mercedes team-mate by just 0.026 seconds.
Red Bull's Max Verstappen could be in contention for pole position after finishing third in the practice standings.
The Dutchman, who escaped action for his collision with Lance Stroll on Friday, was only a tenth off Bottas, setting his best lap on the slower medium tyre compound.
He also set the fastest time of the morning session only for the lap to be scrubbed off by the stewards for exceeding track limits.
Hamilton is bidding to move clear of Michael Schumacher's record with his 92nd career win.
But the Briton, who slid off and through the gravel at turn eight on his fastest lap, will head into qualifying without having troubled the top of the time charts during practice.
AlphaTauri driver Pierre Gasly finished fourth, one spot ahead of Red Bull's Alexander Albon. Ferrari's Charles Leclerc rounded out the top six.
