Pierre-Alain Frau's penalty miss cost Caen a victory which would have provided a huge boost to their Ligue 1 survival hopes.
The forward had spoken in the build-up to the game of the importance of three points, which would have lifted them above their opponents and out of the relegation zone.
But the crucial moment came five minutes before half-time when his spot-kick hit the crossbar, the second time the woodwork had denied the hosts - though Ajaccio also went close when Eduardo's effort was cleared off the line.
Kandia Traore was first to rattle the Ajaccio bar with a 12th-minute effort from the edge of the box. Frau's headed lay-off then set up Frederic Bulot, but Guillermo Ochoa saved his powerful shot with his feet.
Ajaccio responded strongly and, from Ilan's cross, Johan Cavalli drew a reaction save from Alexis Thebaux.
Eduardo went even closer when his 20-yard effort beat the keeper but Jeremy Sorbon was on hand to clear off the line.
Frau should have opened the scoring when Carl Medjani fouled Traore in the box, but his effort was inches too high and it remained goalless at the interval.
The former Lille man sought to atone for his error five minutes after half-time when he spotted Ochoa off his line, but his lob drifted just over the bar.
Benjamin Nivet's 25-yard effort was also just too high and the same player then sent a lob onto the roof of the net.
Ajaccio spied a chance of a late winner but Thebaux blocked Cavalli's shot and also denied Eduardo in the dying minutes.