Valtteri Bottas hailed significant set-up changes to his Williams Formula 1 car after the final free practice session for helping him to qualify fourth for the Spanish Grand Prix.
The Finn skipped first practice so Williams reserve driver Felipe Nasr could participate, and failed to make the top 10 in either of the remaining sessions as he struggled with the handling of his FW36.
But Bottas rallied in qualifying, finding speed in each segment thanks to a substantially revised set-up, which helped him to a best lap less than four tenths adrift of Daniel Ricciardo's third-placed Red Bull, and five places ahead of team-mate Felipe Massa.
"Personally I had a really nice lap in the end, which felt good because it was a difficult weekend so far for me," Bottas said.
"Practice two and three were quite difficult, but we made some quite big set-up changes for qualifying and finally started to get more trust for the rear of the car and that way managed to pick up some speed.
"It required a different driving style, but it came from something I noticed on Felipe's car - some things we were doing differently with the set-up.
"Practice three was so difficult for me I thought it better to make a change than stay as we were because we were struggling."
Team-mate Massa was quicker through the first two segments of qualifying, but rued an error in Q3 that restricted him to ninth on the grid for Sunday's race.
"I had an incredible qualifying: Q1 and Q2 I was competitive, and then in Q3 I just locked the rear tyres braking for Turn 10, went straight out of the line and lost maybe six or seven tenths in one sector," Massa explained.
"I'm really disappointed. Today it was easy to start both cars fourth and fifth so for sure I'm not starting on my [correct] position and I'm disappointed in me.
"It's a shame because everything was going perfect through the whole weekend, but the race is tomorrow and you never know.
"It won't be easy starting ninth, but we'll see. Everything can happen and our car looks a little bit more competitive here."