It was the most dramatic moment in an eventful night in the Italian top flight, with six red cards in four matches and three big-name managers returning to the touchline.
With Fiorentina already down to 10 men, in the 26th minute Abraham slipped through Henrikh Mkhitaryan whose neat finish was given as a goal after a long VAR check.
Nicolo Zaniolo’s second yellow card gave a brave Fiorentina side hope and Nikola Milenkovic levelled the scores on the hour mark.
However great work again from Abraham — who also hit the bar — led to Roma retaking the lead through Jordan Veretout four minutes later, the 23-year-old just about staying onside before rolling a perfect low cross which allowed the French midfielder to slot home.
Veretout made sure Mourinho got three points from his first match in Serie A since winning the league with Inter Milan in 2010 when he rolled home the third in the 79th minute after collecting a brilliant Eldor Shomurodov pass.
“We were good 11 against 11, good 10 against 10, but with 11 against 10 we weren’t that good,” Mourinho told DAZN.
“I liked the spirit, the sacrifice the work we put in after the super difficult match on Thursday. But we had difficult moments that I wasn’t expecting.”