Two goals from striker Marc Richards, one greatly assisted by a howler from Blades goalkeeper Ian Bennett, either side of a Billy Sharp equaliser gave Vale the victory and Blackwell expressed concern at his side's showing.

"We've had enough chances to win by a cricket score," he said.

"But if you don't take them you are going to get punished, I don't care what level you play at. Once again (we have) missed opportunities and we have paid the price."

Blackwell was full of praise for young Vale goalkeeper Chris Martin after he produced a string of fine saves to keep United at bay.

"There were two or three world-class saves there, he can be very proud of himself, I thought he was superb," he added.

Last season's semi-finalists Derby were first-round casualties this season as they let a one-goal lead slip to lose 2-1 away to Rotherham, for whom Paul Warne and Kevin Ellison were on target.

Rams boss Nigel Clough said: "We didn't pass the ball around, but credit to Rotherham for the way they closed us down. We nicked the goal and were looking to get through to half-time, but we didn't."

Plymouth boss Paul Sturrock maintains his side's "comical" defending was responsible for their 2-1 defeat to League One side Gillingham.

Simeon Jackson - who netted a hat-trick against Swindon on Saturday - and Andy Barcham struck within three minutes before half-time to send the Gills through.

Luke Summerfield pulled one back early in the second half but Sturrock continued his record as having never won a League Cup match as Argyle boss in five attempts.

He said: "I must have the worst record of all managers in cup competitions, it's unbelievable.

"There were some basic errors out there and some of it was comical."

Ipswich managed to avoid the same fate as Sheffield United, Derby and Plymouth as they edged past Shrewsbury 4-2 on penalties after a 3-3 draw at the New Meadow.

Sixteen-year-old striker Connor Wickham caught the eye for the Tractor Boys with two goals and his manager Roy Keane said: "I don't know how far this boy can go. It's up to him but he has great potential. He works hard, but we will look after him. It's not good for him or the club to play him every week. Believe it or not he's still growing."

Elsewhere, Wayne Routledge fired a hat-trick as QPR hammered Exeter 5-0 while Preston thrashed Morecambe 5-1 at Deepdale.

Watford needed extra-time before seeing off Barnet 2-0 while 10-man Bristol City sneaked past Brentford 1-0.

Doncaster beat Notts County 1-0 at Meadow Lane and two goals inside the first 25 minutes helped West Brom to a win over Bury at Gigg Lane.