Saints were left to rue missed chances as they slipped to a 2-1 defeat at Birmingham.
Jhon Viafara wasted two great openings and Kenwyne Jones another as defeat at St Andrews left Saints probably needing to win all of their final three games to reach the play-offs.
There was a cagey opening to the game as both sides sparred for dominance.
The first real problem for Saints came on seven minutes when Damien Johnson whipped in a low cross from the right. It came to Nicklas Bendtner at the far post but Alexander Ostlund was strong and did an excellent job of preventing him getting a shot in and Chris Baird was able to clear.
Bartosz Bialkowski had to be quick off his line on 11 minutes to slide at the feet of Johnson to block him from getting in on goal after a through ball from Bendtner.
Birmingham were starting to squeeze on the pressure and Saints had to scramble the ball behind to stop Andrew Cole and Bendtner from finishing while Martin Taylor headed narrowly over at the far post from a corner.
Djamel Belmadi had to head off the line after Radhi Jaidi had won a header from another corner.
Saints created their first opening on 17 minutes when Viafara was played in on the right side of the area but he never looked confident and rather than shooting first time tried to cut inside and allowed Stephen Kelly to make the tackle.
Birmingham came close again four minutes later but couldn't convert a scramble in the six yard box.
But they were dealt a blow on 22 minutes when their captain, the lively Johnson, was forced off with a hamstring injury to be replaced by Rowan Vine.
The Blues were winning corner after corner and causing problems from them but Saints were always able to clear albeit they weren't creating chances of their own.
Gary McSheffrey was the next to waste a Birmingham chance when he blazed a half volley over the bar from inside the area at the far post.
But when Saints did create another chance they were so unlucky not score.
Marek Saganowski got the ball with his back to goal and on 32 minutes laid it back to Danny Guthrie whose low drive from the edge of the area flew past the keeper, smacked the bottom of the post and came out.
But just a minute later Saints were behind.
Perhaps inevitably it came from a corner which was delivered outswinging from the left by McSheffrey onto the head of Jaidi who attacked the ball on the edge of the six yard box and powered it high into the top corner leaving the man on the post with no chance and it was 1-0 to Steve Bruce's men.
Leon Best had an effort from distance on 40 minutes but the keeper was able to get his body behind it and save.
McSheffrey was next to have an effort but again fired over after being played in by Cole.
Saints certainly played better after they had fallen behind but couldn't get a goal.
Half-time: BIRMINGHAM 1 SAINTS 0 At the break George Burley made a double change to try and get his side back into the game.
Andrew Surman and Jones came on for Belmadi and Best in straight swaps.
It almost paid dividends straight away when Guthrie played the ball into Jones just inside the area. He knocked it to his left to create a yard of space and hit a low shot but it was tame and at the keeper who saved.
Kelly became the first man in the book for a foul on Jones two minutes later.
Birmingham were looking nervous and unable to keep possession which was giving Saints increased hope.
Guthrie was the next to have a go from the edge of the area but again the keeper got his body behind it to save.
Birmingham had a succession of corners and almost doubled their lead from the third when Stephen Clemence turned it goalwards but Jermaine Wright was on the near post to clear.
Surman had a chance on 66 minutes but fired over the bar after measuring a half volley from a tight angle.
The game really opened up and Bialkowski kept Saints in it when he saved low down from Bendtner when he was through on goal a minute later.
Saints were relieved from the corner when Bendtner was in the action but headed against the bar.
There was a break in play after Bialkowksi was caught by McSheffrey as the pair went for the ball with the Birmingham man going in the book.
But it didn't affect the keeper who came storming off his line to prevent Cole getting through on goal moments later.
Saints squandered arguably the best chance of the game on 75 minutes.
Saganowski did superbly down the left and got a cross to the far post where the unmarked Viafara mishit his shot well wide.
Burley made a final change a minute later with Pele coming on for Wright.
Saints were still in the game as should have been level after another chance which saw Darren Powell with a free header from a corner from eight yards but he flashed it wide.
Bendtner fired wide for Birmingham before they made another substution with Medhi Nafti replacing Clemence.
But Bendtner made no mistake and seemingly sealed the points with ten minutes remaining.
Cole played the ball through to Bendtner who beat the offside trap, knocked it round the advancing Bialkowski and chased after the ball to roll it into the empty net to make it 2-0.
Saints would have got themselves back into but for some more dreadful finishing.
Guthrie managed to get in a shot in the area that hit the bar and the ball fell to Jones in the centre of goal. He was only six yards out but sidefooted over the bar with an empty net in front of him.
Seconds after Birmingham changed Cole for DJ Campbell, Saints did give themselves a chance with five minutes remaining.
Viafara whipped in the ball from the right and Saganowski made it ten in ten with a free header in the centre of the box.
But, despite some late pressure, it proved to be in vain as Birmingham ran out winners.
For match reaction and pictures don't miss Monday Sport.
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