McLaren are leading the constructor's championship but are only 29 points ahead of Ferrari, with Leclerc an obvious threat and team mate Carlos Sainz qualifying fifth and Mercedes' George Russell sixth.
McLaren's Lando Norris hailed the best qualifying lap of his career after beating F1 leader Max Verstappen to pole position at the US Grand Prix.
The final phase of qualifying was halted, with only Piastri and Haas' Nico Hulkenberg having set times, when Sainz slammed backwards into the barriers at the final corner as he prepared to start his flying lap.
Charles Leclerc won the US Grand Prix in a Ferrari one-two with Carlos Sainz on Sunday as Formula One championship leader Max Verstappen dealt Lando Norris a significant setback in their title battle.
The win was a first for Ferrari in Mexico since 1990 and fourth of Carlos Sainz's career.
Red Bull's Max Verstappen dealt Lando Norris a shattering blow in their Formula One title battle by winning a wet and chaotic Sao Paulo Grand Prix from 17th on the grid.
Formula One world champion Max Verstappen took pole position for a third straight year at the Japanese Grand Prix on Saturday, with Sergio Perez qualifying a close second to ensure a Red Bull front-row lockout.
Red Bull make changes to car after discussions with FIA
Verstappen's hopes of a record-extending 11th successive victory looked a long shot on a city circuit where overtaking is never easy.
Ferrari's Charles Leclerc qualified fourth with Mexican Sergio Perez, Verstappen's closest title rival and team mate but a massive 151 points adrift after 15 of 22 rounds, fifth and 0.773 off his team mate's pace.
Max Verstappen celebrated a record 10th win in a row by leading Red Bull team mate Sergio Perez one-two at Ferrari's home Italian Grand Prix
Max Verstappen put Red Bull on pole position for his home Dutch Grand Prix at Zandvoort for the third year in a row
Max Verstappen added his name to the list of triple Formula One World champions on Saturday after Red Bull team mate and sole title rival Sergio Perez crashed out of the Qatar Grand Prix sprint race.
Ferrari's Carlos Sainz won the Singapore Grand Prix on Sunday to end Formula One leader Max Verstappen's record run of 10 wins in a row.
'We definitely have a lot of positives to take. Finishing second in the first race of the year is a good start. I think we had the pace to fight for the win.'
Mercedes-AMG driver Arjun Maini made history during the first race of the 2021 DTM Championship's season finale when he claimed second place at the Norisring race circuit, becoming the first Indian to stand on the DTM podium.