Blues’ hopes of progressing in this season’s EFL Cup were dashed after they were knocked out of the competition at the first round stage by Oxford United.
But the visitors left it ultra-late to score the decisive goal as they found the back of the net in the last minute of extra-time courtesy of Liam Sercombe
In a game that was somewhat lacking in attacking quality, neither side managed to break the deadlock in regular time.
Gary Rowett made no less than nine changes to his starting XI, with Jonathan Grounds and Michael Morrison the only two players to keep their places from the weekend's home league draw against Cardiff City.
And in a change from his usual team formation, Rowett elected to go with a 4-4-2 line-up, with Jack Storer partnering James Vaughan in a front two.
Leading the line for Oxford was former Blues striker Wes Thomas and in defence ex-loanee Aaron Martin.
The League One outfit started the brighter of the two sides, but it was Blues that had the first chance of note following a corner. Paul Caddis whipped the ball into the box where it was met by Grounds’ header.
The ball was cleared as far as Paul Robinson, but the centre-half should have done better as he sent his shot flying over the bar.
With 21 on the clock Caddis dispossessed an Oxford defender before cutting in with the ball from the right by-line. But with several team-mates waiting to pounce in the box, he took it too close to Simon Eastwood and the Oxford keeper blocked his pass.
Blues were given a scare after Grounds gave away a sloppy foul just a yard outside his own area, but fortunately Chris Maguire curled his free-kick just over the bar.
Oxford were forced into a premature change when Thomas limped off injured before the game had even reached the half-hour mark.
Blues came close to breaking the deadlock twice in a matter of minutes when first Vaughan saw his close-range shot saved by Eastwood and then the Oxford stopper was on hand to deny Solomon-Otabor after he had cut into the area before making an attempt on goal.
Tesche then tried his luck with a snapshot from the edge of the area that was just off target.
Eastwood was quickly back in action for the visitors as he produced a neat diving save to push away Tesche’s well-struck effort
Half-time: Blues 0 Oxford United 0
Blues were lucky not to find themselves behind on 50 minutes when Ryan Taylor was just unable to get on the end of a cross.
The ball was sent back across Adam Legzdins’ six-yard box by Alex MacDonald, but it just evaded Kane Hemmings who was poised to slot the ball home.
With neither side presumably relishing the prospect of extra-time the game appeared to step up a gear and became much more open.
Vaughan glanced a header wide for Blues and then MacDonald shot high and wide for the visitors.
Blues made their first substitution of the evening after 74 minutes when Stephen Gleeson was sent on in place of Kieftenbeld.
Four minutes later Jacques Maghoma and Clayton Donaldson were introduced into the action in place of Caddis and Storer respectively.
Legzdins had to be alert to deny Chris Maguire when the Oxford man tested him with a low shot which would have snuck just inside the post had the Blues keeper not got down to it in time.
Blues were than thankful for the post being in the way when Maguire crossed from the left and Hemming headed goalwards but the ball struck the upright.
With the game deep into stoppage time Sercombe blasted high over the bar in then the same player saw his close-range attempt snuffed out by Legzdins meaning the tie entered extra-time goalless.
Less than a minute after the restart Solomon-Otabor went on a marauding run, but it was ultimately to no avail as he blasted high over the bar with his shot.
Blues were then just a yard away from opening their account when Vaughan swiveled before firing just the wrong side of the post.
It was only a brilliant save from Legzdins’ feet that prevented the hosts from falling behind after MacDonald did well to get a powerful low shot off after collecting the ball on the right of the area and finding his way inside past Grounds.
Although both sides looked to win the contest they were ultimately struggling to find a way through.
But that all changed in the 120th minute of action when Legzdins was only able to palm a cross from the left and Sercombe was there at the far post to head home and send the 1,155 U’s fans into raptures.