Blues were unable to make it three games unbeaten as they suffered a 2-1 defeat at the hands of Nigel Worthington's York City.
A goal in 68 seconds gave York the lead, courtesy of Jamie Reed before Ryan Leonard equalised for Blues. Just before half-time though and York regained the lead through Matt Blair.
That was the way it stayed as York held on, despite late pressure from Blues, to move three points clear of the relegation zone going into the final day.
Phil Brown made one enforced change to his side as Luke Prosser replaced Tamika Mkandawire at the heart of the defence.
Prosser has been out injured since the trip to Wembley but was recalled following Tamika’s return to Millwall.
That was the only change made from Blues’ 2-0 win at Aldershot on Tuesday night as Britt Assombalonga, Freddy Eastwood and Barry Corr continued in attack.
Daniel Bentley kept his place in goal with Paul Smith back from a virus to take his place among the substitutes. Ben Reeves missed out with injury.
Having not conceded in their previous two games, Blues got off to the worst possible start. York broke down the left-hand side and after failing to clear the ball was somehow looped over Bentley courtesy of a deflection off Ryan Cresswell.
Blues first real chance of the game came with 17 minutes gone. Antony Straker collected a loose ball on the left-hand side and crossed well, but Corr’s header was straight at Michael Ingham.
With their next chance, Blues were level. Corr flicked the ball on to Eastwood who cut inside and fired a left-footed shot that took a wicked deflection into the path of Leonard who flicked the ball into the bottom corner with his head.
Both sides were getting forward in numbers whenever they could, and it was York who went back in front. Jack O’Connell’s cross wasn’t dealt with by Blues and the ball eventually fell to Blair who volleyed past Bentley.
Brown made an early change at the start of the second-half as Gavin Tomlin replaced Marc Laird meaning Blues had four strikers on the pitch.
Two of those almost linked up just after Tomlin’s introduction as Eastwood crossed for Corr, but the striker headed straight at the keeper.
Eastwood then shot wide on his left foot before Daniel Parslow headed wide for York from Lanre Oyebanjo’s long throw.
Jason Walker went close to making it 3-1 but saw his shot from 18-yards well kept out by Bentley.
Blues thought they had equalised with five minutes left as Leonard’s cross was headed downwards by Corr and turned into the net by Tomlin, but the flag was up for offside.
With seconds left, Blues again thought they had equalised but Corr's shot was cleared off the line and then Leonard's volley was too as York held on to pick up a vital three points in their fight against relegation.
Blues: Bentley; Clohessy, Cresswell, Prosser, Straker; Laird (Tomlin), Leonard, Lund; Assombalonga (Hurst), Eastwood, Corr.
Subs: Pinnock, P. Smith, Spillane, Barker, Phillips