The Crystal Palace manager barred the way of his beloved Blades as his side earned a scoreless draw at Selhurst Park.
Sheffield United arrived in south east London still harbouring hopes of top-two finish, but only a victory would have given them a chance of joining champions Wolves in the Premier League next season.
Even then, the Yorkshire club had to hope that Reading would take something from their home game against Birmingham.
Conspiracy theorists had been hard at work in the build-up to the game, playing on the fact that Warnock is the former Blades boss, a self-confessed lifelong fan and long-time friend of current Blades manager Kevin Blackwell.
But in the end it was all immaterial as Birmingham won 2-1 at the Madejski Stadium to seal an immediate return to the top flight.
Warnock said: "When I was told about Birmingham winning there was some relief as this result then didn't matter.
"I will get right behind them now for the play-offs and hopefully they can go and finish the job off at Wembley.
"While I am tinged with being a Blade, it was solely a manager's job I had to do. But it wasn't easy for me.
"I shook Kevin's hand before the game and told him that I wanted to win.
"We couldn't manage that, but we competed really well and had some good chances to score.
"I couldn't have asked for anything more from my players."
Sheffield United face Preston in the play-off semi-finals and Warnock expects his old club to be too strong over the two legs.
He added: "Like I said, I can go back to being a Blade now and support them in the play-offs.
"I think once they get over the results this weekend, they will be the favourites to go up.
"I would imagine that over two legs they will be stronger than Preston.
"They are not easy on the eye to watch but they are all committed. You just need a bit of luck but I think they can do it."
Blackwell felt that Sheffield United just lacked some good fortune at Selhurst Park.
The Blades boss pointed to the performance of Palace keeper Julian Speroni, who made three superb saves to keep his side at bay.
Speroni athletically tipped headers over the crossbar from Chris Morgan and Greg Halford in either half.
In between, the Argentinian produced a point-blank save to block Jamie Ward's shot from six yards.
"You need breaks in these games and we just didn't get them - Speroni made save after save," said Blackwell.
"He was the man of the match with three unbelievable saves, and then of course we hit the post.
"We needed something to go our way and it just didn't happen for us.
"I feel we had two good shouts for penalties for fouls on Darius
Henderson, but we didn't get them.
"If I could take anything away from Crystal Palace it would be Lady Luck. I'd put her in the boot of the car and hope that she can rear her head in the play-offs when you need it."
On his side's performance, Blackwell added: "It was a massive pressure game and they didn't buckle, they just kept going.
"I can't complain about the display at all and now we just need to reproduce that in the play-offs."