ASSE looked set to finally beat Lyon on their home turf when Dabo, who also saw red in this fixture last year, was given his marching orders for a headbutt on Max Gradel that was reminiscent of Zinedine Zidane's famous red in the 2006 World Cup final.
But just 10 minutes later Michel Bastos smashed in a 25-yard free-kick before St Etienne's night completely fell apart with the dismissal of substitute Alejandro Alonso.
Lyon's win was sweetened further as they increased their lead at the top of the standings to five points after Marseille suffered a shock 3-0 defeat at home to Lorient earlier today.
As well as looking to end their long winless home record against their fierce rivals, St Etienne had hoped to break into the top three with a victory.
They were instead on the back foot in the opening 45 minutes as their former midfielder Steed Malbranque pulled the strings.
Lyon lost playmaker Clement Grenier to injury early on before Malbranque almost opened the scoring on 23 minutes when he volleyed just wide after Maxime Gonalons sent him through.
Anthony Reveillere skimmed the post moments later after tricking past Faouzi Ghoulam and Loic Perrin before Remy Vercoutre made his first save at the other end to deny Pierre-Emerick Aubameyang.
Lyon continued to push forward after half-time and Bafetimbi Gomis headed a Malbranque corner that Stephane Ruffier blocked.
Dabo's moment of madness followed soon after, however, to leave his side a man short with 35 minutes left.
It mattered not as Bastos sensationally fired them ahead after Alexandre Lacazette was fouled by Fabien Lemoine. Bastos then smacked in an unstoppable free-kick that left Ruffier motionless.
ASSE tried to respond, with a low Francois Clerc shot sneaking past the post, but their hopes were all but ended when Alonso, who had been on the pitch for 10 minutes, saw red for a second caution on 84 minutes.