Antonelli's closest title rival George Russell had to settle for fourth at a windy Silverstone, behind Ferrari's Charles Leclerc and seven-time world champion Lewis Hamilton.
Piastri, who finished fourth at last week's Austrian Grand Prix and currently lies sixth in the drivers' championship, admitted his McLaren car had experienced problems at the iconic English race track.
"Just struggled a lot with rear grip," said the 25-year-old, who finished seventh in the earlier sprint race.
"We thought we made some sensible changes in qualifying but they just didn't have the impact we were hoping for, I guess. A bit of a surprise as to why it has been so tricky this whole weekend."We have been battling with the balance of the car for the whole weekend which normally I feel like we just lack grip and downforce. This weekend it has been a pretty big handful to drive the car. Hopefully we can see what we can do tomorrow and make it a little bit nicer."
Isack Hadjar qualified fifth for Red Bull, ahead of last year's British GP winner and Piastri's McLaren team-mate Lando Norris.
Red Bull's four-time world champion Max Verstappen will line up seventh ahead of Piastri while the Racing Bulls pair of rookie Arvid Lindblad and Liam Lawson completing the top 10 places.
Leclerc was 0.175 of a second slower than the 19-year-old, whose fifth pole of the season extended Mercedes's record of securing the top slot at all nine grands prix so far in the campaign.
"It was a very tidy lap, a lap where I put everything together," said Antonelli, of his best time of one minute 28.111 seconds set after going out first for the final run.
"It was very tricky with the wind because it was very gusty and unpredictable."
Antonelli earlier won the sprint ahead of Hamilton, to go 43 points clear of Briton Russell in the standings.
Winner of five races in a row until Hamilton ended the streak in Spain last month, Antonelli has taken the sport by storm and appears to have the measure of Russell at his home race.
"It's not going to be easy because I have two Ferraris behind me and, for sure, they will work together."
