Blues eased away from the relegation zone with a professional 2-0 away to Peterborough United.
The visitors impressively combated the attacking threat of Peterborough, laying the foundations for goals from Nikola Zigic and Chris Burke in either half, to move them seven points clear of the relegation zone.
Clark made one change to the side that drew with Sheffield Wednesday on Tuesday evening, as Peter Lovenkrands replaced the injured Marlon King (knee) up front. However, Darren Ambrose managed to feature on the bench, having fully recovered from his own knee problem.
The contest in East Anglia adopted a good tempo from the off, with plenty of space for both teams to exploit.
Peterborough created the first chance, when Lee Tomlin dragged his 20-yard effort a couple of feet wide of Birmingham’s goal.
Blues replied with an attack of their own on seven minutes, but Zigic’s looping header was safely held by Bobby Olejnik.
Darren Ferguson’s men then proceeded up the other end of the pitch and had penalty claims waved away, after Dwight Gayle collided with Curtis Davies.
The London Road crowd had to wait until the 19th minute for the first real opening of the afternoon – which fell the way of the hosts.
Wade Elliott’s misplaced pass was pounced on by Tommy Rowe, who played a one-two with Tomlin and saw his shot saved by Jack Butland. The England international then instantly reacted to miraculously tip Tomlin’s follow up attempt over the bar.
Posh were very much on top for a period in the first-half but after Peter Lovenkrands’ 25-yard strike was well held by Olejnik, Zigic broke the deadlock in the 34th minute.
Michael Bostwick’s sloppy clearance found Burke and the Scot cut in from the right and forced Olejnik to parry away his curling shot. But Zigic was on hand to side-foot home his seventh goal of the season from six-yards.
Blues would have doubled their lead if it wasn’t for the crossbar stopping Callum Reilly’s thunderbolt from flying in. Lovenkrands also went close when nudging Mitch Hancox’s cross inches wide of Olejnik’s left post.
The Dane got himself into a great position again the other side of the break, but the former Rangers forward couldn’t quite direct his flicked header on target from Burke’s delivery.
For all their efforts the visitors had to wait for a decisive second, with a sound defensive display needed. And for all of Peterborough’s pressure, the Blues defence held firm.
Rowe looked set to head a cross in from the left, only for Steven Caldwell to get in the way and usher the ball out for a goal kick.
The hosts only other opportunity arrived on 69 minutes, with Tomlin heading Nathaniel Mendez-Laing’s delivery straight at Butland.
And Burke put the game beyond doubt ten minutes from time, when his fizzing strike deflected off Gabriel Zakuani and looped over Olejnik into the net.
Zigic thought he made it 3-0 with a second, but the Serb was ruled offside after tapping home Burke’s cross-come-shot.
Little did this matter, though, as Peterborough couldn’t prevent Blues from rising up to 15th in the table.
Peterborough (in numerical order): Bobby Olejnik, Gabriel Zakuani, Michael Bostwick, Lee Tomlin, Grant McCann, Tommy Rowe (C), Joe Newell (Danny Swanson 61), Kane Ferdinand, Mark Little, Dwight Gayle, Nathaniel Mendez-Laing.
Subs: Joe Day, Craig Alcock, Shaun Brisley, Nathaniel Knight-Percival, Jack Payne, Shaquille McDonald.
Bookings: Bostwick (70)
Blues: Jack Butland, Paul Caddis, Curtis Davies, Steven Caldwell (C), Mitch Hancox, Chris Burke, Callum Reilly (Morgaro Gomis 76), Jonathan Spector, Wade Elliott, Nikola Zigic (Hayden Mullins 90+2), Peter Lovenkrands (Wes Thomas 79).
Subs: Colin Doyle, Paul Robinson, Darren Ambrose, Nathan Redmond.
Goals: Zigic (34), Burke (80)
Bookings: Reilly (60)
Referee: M. Russell
Attendance: 8, 350