In fairness Lee Clark’s side had the better of the chances, but it took a fortunate goal from Wade Elliott after 28 minutes to break the deadlock.
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Clark made no less than five changes to the side that was beaten by Coventry City in the Capital One Cup on Tuesday evening.
Jack Butland, Pablo Ibanez, David Murphy and Wade Elliott all returned to the starting XI.
There was also a first appearance for Paul Caddis just 24 hours after the right-back made the switch to Blues from Swindon Town.
Stephen Carr, Darren Ambrose, Curtis Davies, Keith Fahey and Nikola Zigic all missed out because of injury.
Blues played some neat passing football in the opening stages and it took them just four minutes to fashion their first opening. Marlon King crossed the ball in from the left for Hayden Mullins, but the midfielder headed the ball two yards wide.
Against the run of the play Blues were given a major scare on the quarter-hour mark when Michael Bostwick’s pile-driver of a shot from 30 yards out smashed back off Jack Butland’s cross bar.
Chastened by the near miss Blues began to step it up a gear and David Murphy fired a volley just wide of the Posh goal from ten yards out.
The game was delayed for several minutes after a clash of heads between Marlon King and Posh captain Gabriel Zakuani, which saw both players require medical treatment before being allowed to continue.
As the half progressed Posh began to pose more of an attacking threat themselves and Pablo Ibanez was forced to make a fine tackle on the edge of his own box with danger looming.
Blues took the lead in a somewhat fortuitous fashion after 28 minutes.
Elliott floated a free kick deep into the Posh area which Olejnik attempted to punch ball away, but under pressure from Lovenkrands the ball skidded off his fist and bounced backwards and over the defenders into the back of the net.
Blues had a great shout for a penalty minutes later when Ntlhe appeared to have fouled Lovenkrands as the frontman burst through on goal. But for some reason referee Gavin Ward waved play on and then to compound matters booked the Dane for his protests.
With just a few minutes to go to the break, Posh were awarded a free kick in a dangerous position just five yards outside the Blues penalty area.
The dead ball was passed sideways for Bostwick who tested Butland with stinging shot, but the young England keeper collected the ball at the second attempt.
As the match entered stoppage time at the end of the half, the impressive Caddis went on another run before drilling the ball into the box where it eventually fell to Lovenkrands just ten yards out. But with the goal at his mercy he scooped the ball over the bar.
Half-time: Blues 1 Posh 0
Darren Ferguson made one change at the break with Lee Frecklington replacing Zakuani because of the head injury the player had sustained earlier in the game.
Frecklington almost immediately made an impression as he tested Butland from 20 yards.
But Blues were soon back into their attacking stride. Lovenkrands saw his header saved and then Caddis flashed a shot across the front of the goal.
However, Posh were certainly not devoid of attacking threats and pinned Blues back for several minutes.
With just over an hour on the clock, teenage winger Nathan Redmond was sent on in place of Wade Elliott.
Posh then made their second change with Lee Frecklington replacing Kgosi Ntlhe.
Butland did really well to get his body in the way of Danny Swanson’s shot, with the Posh player looking odds-on to score.
With the game so finely poised there was certainly a feeling of trepidation around St. Andrew’s as Blues looked to claim their first three points.
Gomis joined the action in place of Lovenkrands on 71 minutes as Clark looked to strengthen his side in the middle of the park.
Posh continued to push on in search of an equaliser, but it was King who was next to try his luck with a rasping shot. Redmond then blasted the ball wide.
King was still proving to be a menace to the Posh defence in the closing stages and he wasn’t too far wide with a shot from just inside the box.
Thankfully Blues managed to hold out in a tense final few minutes.
Hopefully the win - however it came about - can provide the kick-start to Blues’ season that boss Clark has been calling for.
Full-time: Blues 1 Posh 0
Blues: Jack Butland, Paul Caddis, Steven Caldwell, Pablo Ibanez, David Murphy, Chris Burke, Hayden Mullins, Jonathan Spector, Wade Elliott (Nathan Redmond, 62), Peter Lovenkrands (Morgaro Gomis, 71), Marlon King.
Subs not used: Colin Doyle, Will Packwood, Mitch Hancox, Ravel Morrison, Akwasi Asante.
Bookings: Lovenkrands (37), Caddis (41), Murphy (45+3).
Goals: Elliott (28).
Posh: Bobby Olejnik, Shaun Brisley, Gabriel Zakuani (Lee Frecklington h/t) , Michael Bostwick, Danny Swanson (Emile Sinclair, 79), Lee Tomlin, Tyrone Barnett, George Boyd, Grant McCann, Mark Little, Kgosi Nthle (Craig Alcock, 63).
Subs not used: Joe Day, Joe Newell, Nat Knight-Percival, Jonson Clarke-Harris.
Referee: Gavin Ward
Man-of-the match: Paul Caddis
Attendance: 14, 926 (629 away fans)