The 60-year-old Ulsterman launched his reign with a hard-fought 2-1 Barclays Premier League victory over Blackburn on December 11 to spark a revival which has assumed ever more impressive proportions as the months have passed.
He heads for Ewood Park for the reverse fixture on Tuesday night with the Black Cats sitting ninth, and a replay away from booking an FA Cup semi-final date with Carling Cup winners Liverpool at Wembley.
Sunderland have lost just four of the 19 games for which O'Neill has been in charge to date, and he knows things could hardly have gone much better.
Asked if he could have envisaged the current situation, he said: "No, I could not. I wouldn't have envisaged us being even in the semi-final draw, for what it's worth.
"We still obviously haven't passed the quarter-final stage, but to be actually in a semi-final draw and at least to know who you might play if there was a possibility of getting through...
"But more importantly than that, the number of points we have been able to accumulate, I wouldn't have envisaged that at all."
O'Neill took over from Steve Bruce with the Black Cats having collected just 11 points from their first 14 league games.
They will run out at Blackburn having added a further 26 from their subsequent 14 fixtures, and are a single win away from the 40-point mark generally accepted as the safety target.
Even O'Neill, who has spent much of his time at the Stadium of Light to date insisting his side was engaged in a relegation battle, concedes that victory in Lancashire would complete his first mission.
He said: "I think now that 40 points this season will definitely secure survival in the Premier League.
"With the sides now in the positions that they are in, I think it would take a lot now for those sides to achieve 40 points.
"The truth is this year, if you were to give any of the bottom five 40 points, obviously they would take that in a trice."
Blackburn, of course, are one of those bottom five teams despite a recent rally which has lifted them three points clear of the drop zone, although O'Neill believes their cause is far from forlorn.
He said: "Their run has been great. They won at Old Trafford and I am quite sure with the best will in the world, they wouldn't have been expecting to have done that, and that will have given them a big boost.
"The results just after that might not have gone their way, but to win that game, that's three points you wouldn't have expected.
"During the course of the season, teams will be able to find a game where something turned for them, either positively or negatively.
"From their viewpoint, that win at Old Trafford was theirs."
Right-back Phil Bardsley has a fighting chance of playing despite suffering from bruised ribs, but left-back Kieran Richardson has been ruled out with a calf problem once again.
The game will take place with all eyes on the condition of Bolton midfielder Fabrice Muamba following his collapse at the weekend, and with Sunderland having adopted a full cardiac screening policy for players in 2008.
O'Neill said: "The medical staff here feel they do have very, very stringent tests. I think they are forerunners in that, and that's great credit to them.
"I wasn't aware of that when I joined the football club and that's obviously excellent news."