Red Bull's Max Verstappen on course for third title as Qatar sprint looms
McLaren's Australian rookie Oscar Piastri took pole position ahead of teammate Lando Norris for the 100km race at the floodlit Lusail circuit.
The race is a standalone event, with the main grand prix on Sunday.
Verstappen needs to finish only sixth in the sprint - and take three points - to secure his third successive world championship.
Perez, 177 points behind, must meanwhile finish in the top three to have any hope of delaying the inevitable for another day.
"He (Verstappen) is not interested in the three points. He's interested in the maximum points," Red Bull team principal Christian Horner told Sky Sports television.
"He's a racer, that's the way the team is attacking this weekend. We will give it our best shot and I think we will have an interesting race today."
Mercedes' George Russell will line up in fourth place with the Ferraris of Carlos Sainz and Charles Leclerc fifth and sixth.
Nico Hulkenberg qualified seventh for Haas with Aston Martin's Fernando Alonso ninth, after having a faster time deleted, and Alpine's Esteban Ocon qualifying 10th.
Only the top eight score points in the sprint.
"Max is only starting third, so he's not a million miles away. We will try our best," said Piastri.
The Australian joked he would give the governing FIA five minutes to be sure he was on the pole, after being dropped from third to sixth in Friday's qualifying for Sunday's race due to exceeding the track limits.
Norris was second in Friday's qualifying but dropped to 10th on Sunday's grid for the same offence, and he was not happy with Saturday's performance either.
"Should have been on pole yesterday, should have been on pole today but I'm not," he said.
"Just mistakes, not putting the lap together when I need to. Easily quick enough for pole, I'm just not putting it together for pole."
Mercedes' seven-time world champion Lewis Hamilton will line up only 12th on the grid for the 19-lap race.
The session started 20 minutes later than scheduled due to an extra practice session that became necessary after track limits were changed following a warning from tyre supplier Pirelli about damage caused by kerbs.