George Russell built confidence ahead of the Barcelona-Catalunya Grand Prix by topping the timesheets in the final practice session on Saturday.
The Mercedes driver has endured some difficult weeks but has led the way in two of the three practice sessions at Montemelo.
McLaren's Oscar Piastri followed, two tenths of a second behind, with Ferrari's Charles Leclerc third and 2025 champion Lando Norris fourth in the other McLaren.
Lewis Hamilton was fifth but seven-tenths down on Russell, ahead of Max Verstappen in sixth and championship leader Kimi Antonelli.
Teenage sensation Antonelli, seeking a sixth straight Grand Prix triumph on Sunday, was left frustrated by traffic.
The 19-year-old Italian's first qualification simulation lap was spoiled by the slow moving Lance Stroll, and on his second there were several cars blocking his way.
"Why do I always get traffic? I don't understand," he complained over the team radio.
In a slow start to the third practice session, only Cadillac duo Valtteri Bottas and Sergio Perez took to the track. Audi's Nico Hulkenberg soon joined them.
After around 20 minutes, several other riders came out of their garages, although the Mercedes, McLarens and Ferraris waited even longer to emerge on another hot, sunny day.
Home fans were happy to see veteran Fernando Alonso, cheering him on from the grandstand named after the two-time world champion, ahead of what he says is probably his last race at Montmelo.
Norris was fastest on Friday from Russell and Piastri, and he leapt to the top of the timesheets on Saturday with a lap of 1:16.609.
Briton Russell, who has been overshadowed by team-mate Antonelli this season, responded with a time of 1:16:258 to go top. Antonelli followed him 0.242s behind.
Ferrari's Hamilton, who secured a podium at Monaco last weekend, struggled on his first flying lap at nearly nine tenths slower than Russell.
There was a red flag when Bottas beached his Cadillac in the gravel going into turn 11, telling his pit wall he had lost his brake pedal.
Russell improved further to 1:15.679, although Friday's pace was not matched.
Audi duo Hulkenberg and Bortoleto came in eighth and tenth, either side of Racing Bulls' Arvid Lindblad.
Qualifying takes place at 4pm local time (2pm GMT) Saturday afternoon.