He fouled Nicolas Jackson and, having been initially been shown a yellowcard and a penalty given, the video assistant referee ruled the foul was outside of the box but upgraded his yellow to red.
Palmer had given Chelsea the lead in the first half, scoring a Panenka penalty after Lorenz Assignon received a second yellowcard for fouling Mykhailo Mudryk in the box.
The Foxes, who went into the game with a five-point advantage, looked set to hold out for a vital draw as a thrilling game went into injury time, despite being reduced to 10 men after Danny Simpson was sent off for a second yellowcard early
He was booked for taking off his shirt to celebrate and shown a second yellow shortly after for a dive - before Marco Asensio scored an excellent third.
They were made to pay for their ill-discipline here on Sunday when Aston Villa condemned them to yet another dismal home defeat after right-back Malo Gusto saw his yellowcard for a poor challenge on Lucas Digne upgraded to red following a VAR
Arsenal's Francis Coquelin was sent off after 55 minutes after receiving a second yellowcard for a foul on Harry Kane, leaving the door open for Spurs to respond with two quick goals.
Inter held out for the remainder of time, but it was put truly to bed when Atalanta substitute Rafael Toloi was given a second yellowcard for pulling Alexis Sanchez back.
There was further drama to come in injury time as Newcastle were reduced to 10 men when Gordon received a second yellowcard for kicking the ball away, but they managed to hold out for a victory that could prove vital in their pursuit of European
Pjanic was booked just before half time and received a second yellowcard for handball in the 72nd-minute as Roma's five-match winning run in the league came to an end.
They were reduced to 10 men when Reece James was shown a second yellowcard for a foul on Gordon, before the former Everton man completed the scoring late on.