Chelsea eased to a resounding Champions League win at Stamford Bridge, where their opponents played most of the match with 10 men.
Timo Werner scored with two penalties and Tammy Abraham also netted for the Blues, who were without Kai Havertz after the German tested positive for Covid-19.
Havertz tucked away his first spot-kick after being tripped by Dalbert near the edge of the penalty area.
And Rennes had every reason to feel aggrieved when another penalty was awarded four minutes before half-time after Abraham’s shot ricocheted off Dalbert’s leg and onto his arm.
As if that decision – made after the referee studied the pitchside monitor – wasn’t harsh enough, Dalbert, booked for the foul which led to the first penalty, was shown a second yellow card and sent off.
Werner ruthlessly scored from the spot again and there was no way back for the French side, who fell further behind when Abraham finished from close range after being set up by Reece James’ low cross early in the second half.
Keeper Edouard Mendy, playing against his former club, produced a fine late save to deny Clément Grenier and has now kept five consecutive clean sheets – the first Chelsea keeper to do so since Petr Cech in 2010.
Chelsea: Mendy, James, Silva (Rudiger 68), Zouma, Chilwell (Emerson 62), Kante, (Kovacic 62) Jorginho, Ziyech (Hudson-Odoi 75), Mount, Werner, Abraham (Giroud 62).
Subs not used: Alonso, Christensen, Caballero, Tomori, Azpilicueta, Ziger.