The match looked like it would end in a PSG victory, with Neymar scoring an early second-half goal. However, things took a turn for the Parisians when substitute Marco Verratti was sent off shortly after the goal.
Reims, who were determined to secure a result, got the draw they richly deserved when on-loan Arsenal striker Folarin Balogun broke away to fire home a remarkable 96th-minute equalizer.
The result extends Reims' unbeaten run to 14 games between league and cup and solidifies their mid-table position.
Reims, coached by 30-year-old Belgian-born Englishman Will Still, has a collective strength that allows a team of hungry young players to hold their own against PSG's superstars.
PSG's form has been a concern, as they have now dropped points in three of their four league games in 2023. Despite being three points clear of Lens at the top of the table, they will face a tough challenge in the first leg of their Champions League last-16 tie against Bayern Munich in just over two weeks.