Les Rouges et Noirs twice took the lead at Route de Lorient, but could not play out a victory that would have seen them close the gap on Christophe Galtier's men to three points.
"It was a nice match to watch, with both teams going forward, but there is disappointment," the club's official website quotes Antonetti as saying.
"In the second period, they were really shaken. Stephane Ruffier is a great goalkeeper, but we should have been more effective."
Rennes remain eighth in Ligue 1.