Frank Lampard's side got off to the perfect start when Timo Werner won and converted a penalty in the opening 10 minutes. The Germany international was fouled by Dalbert but dusted himself off to open the scoring from the spot.
The game-changing moment came in the 37th-minute when Tammy Abraham shot into Dalbert's arm. After consulting the pitchside VAR monitor, referee Felix Zwayer awarded Chelsea a second penalty of the evening and sent off the Rennes man for a second yellow card, his first having come when he fouled Werner for the earlier penalty.
"I am happy, I am happy Jorginho is cool with it. It is another point that speaks for our team, we are not selfish. We all go in one direction which is good," Werner told BT Sport.
Chelsea, who were without Kai Havertz after he tested positive for COVID-19 prematch, controlled proceedings and added a third goal five minutes after half-time when Abraham tapped in Reece James' cross from the right.
The comfortable victory left Chelsea top of Group E, ahead of Sevilla on goal difference, with three of the six games played.
It also represented a fifth clean sheet in a row for Chelsea who appear to have fixed the defensive frailties that dogged them last season and in the opening games of this campaign.
"We had a very good game today," Werner said. "Also good for me is we had one more player on the pitch and could control it from behind."
Chelsea goalkeeper Edouard Mendy, bought from Rennes in September to replace the out-of-form Kepa Arrizabalaga, had little to do against his former team mates until the 84th minute when he parried a shot by Clement Grenier.
"OK, the referee gives the second penalty but I think the red card was tough because he didn't do it on purpose. We continued to work hard but that was tough for us," Rennes midfielder Benjamin Bourigeaud said