The warning signs were there from the night before at Roots Hall when Southend sent Manchester United out of the competition. Port Vale did not roll up at the Lane to make up the numbers and were battling it out until the reward of the opening goal came along just after the hour.
There was a nervy period when we were forced to contemplate the possibility of following United out of the Cup before Tom Huddlestone settled anxieties with his first goals for the club - one in normal and one in added time. Jermaine Defoe later put a gloss on the scoreline.
It was a case of three debuts and a return on the night, Andy Barcham being joined on the pitch by Dorian Dervite, Steed Malbranque and a player who began his first team career over two years ago in the shape of Phil Ifil.
Only Michael Dawson was retained from the team that overcame Chelsea on Sunday, a more experienced hand to partner Dervite - a strong, powerful central defender who has impressed in the reserves this season following his transfer from Lille. The 18-year-old probably knew from the off that he would be in for an examination, given the fact that Vale operate with two strikers who must be up approaching Peter Crouch, height-wise.
Dervite actually had a chance to score early on when he was well positioned to profit from the rebound after Lee Young-Pyo tried his luck from distance, but it was not to be.
Defoe came mighty close to breaking the deadlock on midway through the first half when he embarked a jinking run forward and spotted visiting keeper Mark Goodlad off his line. Defoe applied a measured chip, but the keeper recovered himself and managed to palm the ball away.
Malbranque was becoming a clear and present danger to Vale after he eased himself into the game, while it was Huddlestone who was next to try his luck with a drive from distance that flew just wide. There was lots of possession and attempted thrusts forward, but Martin Foyle's side were standing firm and not at all pressed into panic mode.
A deflected Ifil cross caused momentary alarm for Goodlad shortly before the break and it took a good save a few minutes later to deny Defoe again.
The opening minutes of the second half followed much the same pattern as the first until Defoe took nearly decisive action by storming forward and smashing in a low bouncing shot that Goodlad did very well to turn away.
A bumper Carling Cup crowd - 34,560 - inside the Lane were now calling for one Aaron Lennon. They got their wish on 62 minutes and the noise levels instantly increased.
What also happened was that a ball into our box was latched onto by Leon Constantine, who made a decent enough connection to prod the ball through Radek Cerny's legs and sent the visiting throng of Vale fans into raptures.
Dimitar Berbatov was introduced on 66 minutes in place of Barcham to partner Defoe up front, swiftly followed by Hossam Ghaly's introduction for Danny Murphy.
It certainly livened things up and Berbatov was nearly straight on the scoresheet with a downward header from Huddlestone's free-kick - saved by Goodlad. The keeper was in action again when Defoe spun in the box to work himself a shooting opportunity, but the angle as well as Goodlad defeated the little striker.
Lennon then zapped the ball across the face of the goal after a trademark dash down the left, but the toe of Defoe was a little late in arriving for a tap in.
The relief was tangible after 78 minutes when the equaliser came. A free-kick from Huddlestone was pinged into the area and, at first, it looked like taking a diversion off the head of Dervite, but the ball hit the inside of the post before clipping Goodlad and ending up in the net.
The wind was taken out of the Vale sails and Defoe nearly capitalised with a dipping drive with six minutes left on the clock that fizzed just over the bar.
There were no further gains and extra-time was signalled by referee Mr Bennett.
The advantage was nearly registered in the first minute of the extra 30 when Lee crossed low from the left into the feet of Berbatov who reacted instantly and forced an excellent stop out of Goodlad high and close to his right-hand upright.
Eight minutes in and the lead was secured. A Davids cross in from the left was headed back in the direction of Huddlestone by Berbatov and the midfielder drilled in first time. His power-shot did take a deflection off Richard Walker to help it past Goodlad, but that should not detract from the quality and precision of the strike.
One minute after the re-start in extra-time, Ifil pushed forward and delivered an inviting cross that Defoe pounced on and steered past Goodlad to finally end the Vale resistance.
It was a bit of a bumpy ride, but we now take our place in the draw for the quarter-finals on Saturday.
A place in the Carling Cup quarter-finals was booked after Port Vale were defeated 3-1 after extra time on Wednesday night.