The Algerian winger tucked away a cross from Jamie Vardy in the 34th minute to earn Leicester a third successive 1-0 victory and bring a staggering title triumph a step closer.
Second-place Tottenham Hotspur can trim Leicester’s lead back to five points if they beat Bournemouth on Sunday, while third-place Arsenal remain 11 points off the pace despite winning 2-0 at Everton.
Elsewhere, Cesc Fabregas scored two equalisers, the second an 89th-minute penalty, as West Ham United were prevented from climbing to fourth place in a 2-2 draw at outgoing champions Chelsea.
The result left Slaven Bilic’s side in fifth place, a point below Manchester City, who entertain sixth-place Manchester United in Sunday’s derby.
After losing out to Palace goalkeeper Wayne Hennessey in an earlier one-on-one at Selhurst Park, Mahrez put Leicester ahead by steering in Vardy’s low, drilled cross from the left.
Palace had threatened to ignore the script prior to that, Wilfried Zaha volleying wide from Yannick Bolasie’s cross, and it took a smart save from Kasper Schmeichel to prevent Bolasie equalising with a deflected shot.
Leicester nonetheless looked the more threatening team, with Hennessey parrying Marc Albrighton’s low drive and Shinji Okazaki twice going close either side of half-time.
But the introduction of Bakary Sako enlivened Palace and Alan Pardew’s men came within a whisker of equalising in the second minute of stoppage time, only for Damien Delaney’s volley to hit the bar.
Knocked out of the FA Cup by Watford and the Champions League by Barcelona earlier this week, Arsenal bounced back with a one-sided victory over Everton at Goodison Park.
Danny Welbeck put Arsenal ahead early on, rounding Joel Robles to score after a neat build-up, and 19-year-old Alex Iwobi scored his first goal for the club in the 42nd minute after racing onto Hector Bellerin’s pass.
Chelsea narrowly avoided joining Arsenal, Liverpool and Manchester City on the list of major scalps that West Ham have claimed on the road this season.
Manuel Lanzini curled in a glorious shot from outside the box to put West Ham ahead in the 17th minute, only for Fabregas to equalise with an equally picturesque free-kick in first-half injury time.
Substitute Andy Carroll restored the visitors’ lead from Dimitri Payet’s perfectly weighted through-ball, but Fabregas had the final say from 12 yards after Michail Antonio was deemed to have fouled Ruben Loftus-Cheek.
Robbie Brady scored as Norwich City climbed out of the bottom three with a 1-0 win at West Bromwich Albion, meaning Newcastle United and Sunderland will both be in the relegation zone at kick-off in Sunday’s derby.
Meanwhile, Jonathan Walters scored one goal and created another for Joselu as Stoke City won 2-1 at Watford, who replied through captain Troy Deeney’s late header.
