Birmingham City sealed their place in the FA Cup fourth round despite a late scare at Cambridge United on a misty Saturday evening at the Abbey Stadium.

Blues were 3-0 up with just 10 minutes of the tie remaining, thanks to first-half goals from January signing Kai Wagner, Kyogo Furuhashi and Marvin Ducksch.

However, two late goals from Cambridge's Sullay Kaikai set up an exciting - and, for the visitors, nervy - finish.

Birmingham, 14th in the Championship and 40 places above League Two opponents Cambridge, had appeared to be in complete control but the U's - chasing promotion and an immediate return to League One - ensured it was not a straightforward finale.

The underdogs began confidently and should have taken the lead when Mamadou Jobe created a chance for Ben Knight near the penalty spot, but he could not keep his strike below the crossbar.

Birmingham took advantage of that reprieve and led just after the half-hour mark.

Ducksch was selfless in teeing up strike partner Kyogo when the German might have elected to shoot instead and, when the Japanese forward failed to apply the finishing touch, left-back Wagner – making only his second Blues appearance - hammered in the follow-up.

The visitors doubled their lead just before half-time. Kyogo, whose only goal for the club prior to Saturday came in the Carabao Cup in August, robbed Zeno Ibsen Rossi just inside the hosts' half and, with still plenty to do, his finish was assured.

Kyogo ought to have doubled his own tally swiftly after the restart when defender Christoph Klarer picked him out from deep, but he clipped the post with a cheeky dink which had goalkeeper Jake Eastwood beaten.

Rather than crumble, Cambridge rallied and ought to have forced themselves back into the tie when James Brophy's miscued effort found its way into the path of Knight, whose shot again carried too much power.

The hosts huffed and puffed but Birmingham assumed control when Ducksch punished a defensive lapse after having been played in by Tommy Doyle.

Birmingham did slip up defensively themselves before the end as Louis Appere forced Phil Neumann into an error and Kaikai was on hand to profit and pull one back for Neil Harris' side.

Substitute Kaikai then fired in his second with a minute of normal time remaining after Jobe nodded down a free-kick at the back post but Birmingham held on under pressure in stoppage time to go through.

Cambridge United manager Neil Harris told BBC Radio Cambridgeshire:

"I'm really proud of the players. It was a really strong performance. When we were 3-0 down I was stood there thinking 'how are we 3-0 down?' Other than [them] being ruthless with the few chances they created? We'd played so well.

"Then we get back to 3-2 with two really good goals by Sullay and we have a bit of a barnstorming finish – we just couldn't find that chance in injury time to get us back into the game.

"I thought some of the individual performances were outstanding. Mamadou Jobe, George Hoddle – I thought they were outstanding. Sullay came on and really impacted the game for us.

"It's a strong performance and it showed why we've been 14 games unbeaten, in the way we moved a really strong Championship side around the pitch."

Birmingham City manager Chris Davies told BBC WM:

"I said to the players that today was all about 'can we win after winning and build that momentum?' We got a great win last week and today was about continuing that with another win, and that winning feeling on the bus back to Birmingham. We've got it.

"It was difficult conditions. It was one of those nights when it wasn't going to be too fluent and we could tell that, by the conditions, but we got ourselves in a great position and then we had an unnecessarily stressful finish for the last 10 minutes – that's the FA Cup for you.

"We've had plenty of games this season where we've deserved so much more and we haven't [got it]. Today, we deserved to win – absolutely – and we did, and we're through to the next round."