The nation have not qualified for a major tournament since the 1986 World Cup and hopes are high that they can end 30 years of hurt by sealing a place in France next year.
Saturday’s tense goalless draw with Group F front-runners Romania kept them in second place on 13 points – two ahead of Hungary and seven clear of the fourth-placed Faroe Islands.
A play-off place now seems to be the least manager O’Neill can expect but September offers the chance to lock down automatic qualification.
A trip to the Faroes comes first, followed by a Windsor Park date against Hungary, and the stakes are high.
“I always felt the two games in September were crunch games and that’s going to be the case now,” said O’Neill.
“There’s everything to play for. The Faroes are actually fourth now and have had a great campaign for a nation of their size.
“They’re probably thinking that three points against us moves them into a nice position so we can’t disregard them.
“That becomes a very important game now and then we have Hungary at home. It’s a very interesting double header.”
Victory over Romania would have put Northern Ireland in a near impregnable position, but visiting goalkeeper Ciprian Tatarusanu repelled efforts from Jonny Evans, Kyle Lafferty and Oliver Norwood to preserve the stalemate.
That is still a creditable result against opponents ranked 12th in the world and O’Neill was particularly heartened by the efforts of two relative newcomers on the international stage.
Hamilton keeper Michael McGovern and Brentford winger Stuart Dallas both impressed on their first competitive starts and are now ready to challenge on a regular basis.
McGovern was drafted in after No 1 Roy Carroll was ruled out with abdominal pain and was an assured presence.
“I didn’t have any concerns about Michael,” said O’Neill. “In this past he’s probably played at a level which he was better than.
“When he was playing in Scottish Championship I felt he was better than that and he’s proven that with a great season in the SPL.
“If you asked most managers in Scotland I think most of them would name Michael in the top two or three keepers in the division.
“He dealt with everything he had to and I was delighted for him to acquit himself so well in a big game like this.”
Dallas, meanwhile, forced his way into the starting XI with eye-catching friendly displays against Scotland and Qatar and looks set to stay there.
“Stuart has come in after some unfortunate injuries and given us real strong dimension on left side,” O’Neill said.
“He has power and pace, he has defensive strength to his game and he gives us real competition now for the likes of Niall McGinn and Paddy McCourt.
“Bit by bit I think we’re finding we have more players now who can affect games for us at this level and that is just what we need.”