The sales of periodicals to the direct market was not able to beat last year's New 52 relaunch month, reports ICv2.
Graphic novel sales rose by 14.4%, totalling a 1% combined increase compared to last year.
DC Comics dominated the top ten and overall sales, taking 36.4% in dollar share against 31% for Marvel Comics, and 41% in units compared to Marvel's 33.7%.
Avengers Vs X-Men #11 was the bestselling comic of the month according to estimates. The other nine top slots were taken up by issues from DC's zero month including Batman #0, Justice League #0, Green Lantern #0 and Earth 2 #0.
Year to date comparisons continue to show growth in 2012, with comic sales up 17.1% and graphic novel sales up 14.2%, making for a total increase of 16.2% over 2011.
Marvel's Thanos Quest was the bestselling graphic novel in September, followed by DC's The Judas Coin and Image Comics' The Walking Dead vol 8 hardcover.