Max Verstappen set an impressive pace in the final practice session for the French Grand Prix as Lewis Hamilton finished only fifth.
Verstappen, fastest in Friday's concluding running, ended the final action before qualifying seven tenths ahead of Valtteri Bottas.
Ferrari's Carlos Sainz was third with Sergio Perez fourth, nearly a second slower than his Red Bull team-mate.
On Friday night, Hamilton admitted he faced an uphill challenge to wrest the championship initiative back from Verstappen after claiming there was something fundamentally wrong with his car.
Hamilton has been given Bottas' old chassis for this weekend's race at Paul Ricard and on the evidence of practice the seven-time world champion is struggling for pace.
Hamilton, who trails Verstappen by four points in the standings, finished the one-hour running on Saturday morning 0.966 sec slower than his title rival.
Verstappen would have won at the last round in Azerbaijan but for a tyre blowout with just five laps remaining. However, the Dutchman appears in a strong position to avenge his misfortune in Baku.
Elsewhere, British driver Lando Norris finished sixth for McLaren, ahead of Alpine's Fernando Alonso and Esteban Ocon.
Qualifying for Sunday's race gets under way at 2pm.
