An Odion Ighalo brace followed Luke Shaw’s opener to send United through to an away tie against Norwich City in the last eight.
But Derby captain Rooney would not be so lucky, even as United fans chanted: “If Rooney scores, we’re on the pitch”.
The 34-year-old came close to opening the scoring with a free-kick after 18 minutes, only for Romero to palm his attempt away from the bottom left-hand corner.
And Romero would not even allow his old team-mate a late consolation, clawing another free-kick away from goal in the closing stages.
“Sergio was not in a kind mood,” Rooney said after the final whistle. “He could have let that one in. It would have been nice it wasn’t to be.”
Rooney was disappointed not to score but more frustrated with Derby’s failure to reach the last eight.
“Obviously Man United are a good team and we wanted to try and win. I think the draw was favourable for ourselves or United, whoever got through.
“They were the best team on night but for our younger lads, what an experience for them. Although we lost it will do them a world of good.
“That’s the level. The difference in them handling the ball. We try had to try take out moments. We didn’t let anyone down tonight, gave everything and unfortunately came short.”
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