Warnock, who is suffering from a virus, listened to the match on the radio and stayed in touch by phone with Jones and fellow coach Ronnie Jepson.
And despite this the Leeds boss had a decisive impact on the game as he ordered El-Hadji Diouf and Sam Byram to be brought on after Birmingham had gone ahead through a Wade Elliott strike.
The move helped change the flow of the game and Luciano Becchio equalised after an hour to earn a replay.
Jones said: "Neil was in constant touch with us during the game. He made the decision to change the team at half-time and it worked.
"We hadn't created anything from wide positions. Becchio and Ross McCormack needed the ball in the box and they got it in the second half.
"Luciano missed a good chance before he scored but he doesn't freeze and went on to take his next chance so well."
Jones revealed he expects top-flight clubs to come in for top-scorer Becchio and young defender Byram.
"If I was a Premier League manager I would be chasing them," he said. "All the top clubs are watching Sam. They would be daft if they weren't, but we have to keep those two and I think we will."