After opening the Ligue 1 season with three straight draws, PSG has now won three on the spin to muscle its way into the top three.
A brace by
Toulouse rescued a point in extraordinary fashion as goalkeeper
The away side led twice through
But just when an away win seemed certain, Ahamada went forward for a last-gasp free-kick and powered in a header to send the home fans into a frenzy.
Promoted Reims continued its solid start by inflicting a 2-0 defeat on Nancy.
Troyes' winless start continued as Sochaux condemned the promoted side to its fourth defeat in six outings after its return to the top flight.
Sebastien Roudet, Thierry Doubai and Cedric Bakambu were on target for Sochaux, which climbs out of the relegation zone thanks to the 3-1 win.
Elsewhere, Brest moved up to eighth after coming from behind to beat 10-man Valenciennes 2-1.
The away side took the lead through Mathieu Dossevi after 10 minutes and it took until the hour mark for Brest to get back on level terms through
Ten-man Lorient left it late to secure a 1-1 draw against Nice.
The visitor led for much of the match through Camel Meriem's first-half goal and the dismissal of Gregory Bourillon did little to ease Lorient's nerves.