O'Neill's team were beaten 2-0 by Azerbaijan on a dreadful night in Baku, underlining rather than avenging last month's similarly depressing 3-2 reverse in Luxembourg.
The result, courtesy of goals from Rufat Dadasov and Mahir Shukurov, means Northern Ireland have taken just two points from a possible 12 against the two lowest ranked teams in their World Cup qualifiying group, and they now have just one match to avoid an embarrassing bottom-placed finish.
O'Neill has had rather too many disappointing results to reflect on in his first campaign in charge but gave a measured assessment after the latest installment.
"It's another harsh lesson, the players have made it difficult for themselves in this campaign," he said.
"I'm not going to turn around and say we've been progressing at a rate of knots. We're progressing in small steps and taking a few setbacks along the way. This was another one.
"Some of our performances have been good but we just have to live with the results and they've been poor, there's no getting away from that."
The result was compounded by Jonny Evans' injury-time red card for a crude foul that led directly to Azerbaijan's second.
Evans will now be suspended for Tuesday's campaign-ending clash in Israel, alongside Gareth McAuley, who was booked for talking back to the referee, and Oliver Norwood.
O'Neill declined to hold his tongue on those incidents, though insists his side have been harshly treated by officials over the course of the qualification group.