Gary Harkins' return to the Kilmarnock team was the key to the Ayrshiremen's 2-1 cup replay win over Dundee, according to manager Kenny Shiels.
Harkins was expected to be out for six weeks after breaking his ankle training at New Year but he set up both of Killie's goals in his surprise start.
"Gary Harkins was fantastic. I am really pleased for him against his old club," Shiels told BBC Scotland.
"He was the pivotal point of the team, I felt."
Killie will head to Easter Road to take on Hibernian in the Scottish Cup fifth round, thanks to well-taken first-half goals by Paul Heffernan and Dean Shiels.
Gavin Rae headed a goal for First Division Dundee to make it 2-1 after 63 minutes but Kilmarnock held on to keep Barry Smith's side at bay.
Shiels added: "Dundee were as good as us. They did the First Division proud tonight.
"We started poorly but [improved] once we got in control of our passing.
"I think it is a fantastic result against a team that hasn't been beaten on its travels since September. We knew it was going to be difficult.
"Dundee had good possession at times but our boys were magnificent.
"We did well - the organisation of my two centre-halves, the triangle in the middle of the park, Garry Hay played well.
"Overall, I would say we deserved to go through and that is a fantastic achievement."
The Northern Irish manager of the Scottish Premier League's sixth-placed side was keen to look ahead to the weekend visit of bottom club Dunfermline.
"Dunfermline are fighting for their lives: so are we, we're not out of the relegation [fight] yet," said Shiels.
"We've got to be up for this one on Saturday. That is what we turn our attention to now."