Bristol City were plunged deeper into relegation trouble as they crashed to defeat at the hands of fellow strugglers Peterborough in this Championship basement battle at London Road.

Once again, the Robins contributed to their own downfall, changes in team selection and shape leading to a confused first-half performance.

Manager Derek McInnes made changes at half time and the Robins revived briefly, only to finish well beaten.

Without a win in eight games, Posh took full advantage of the visitors' shortcomings to secure their first three-point haul of 2012.

Lee Tomlin started and finished things, heading the home side in front after just eight minutes and scoring Peterborough's third goal five minutes from time.

David Ball netted in the 62nd minute and City were left to wonder what might have been had Stephen McManus's header not been cleared off the line by Lee Frecklington when Posh were 1-0 up early in the second half.

To make matters worse, McManus hobbled off shortly after Peterborough had gobne 2-0 up, adding to City's mounting casualty list.

A fourth defeat in five games leaves City four places off the foot of the table, but they are now just three points clear of third-from-botto m Nottingham Forest, who have a game in hand.

Having fallen behind in each of their last four games, City were concious of making a better start at London Road. Yet, despite the best laid plans, the visitors conceded after just eight minutes.

Play-maker-in-chief George Boyd proved the architect-in-chief, turning inside the penalty area to send a rising shot past David James and towards goal. Robins skipper Liam Fontaineaverted any immediate danger by heading off the line, but Lee Tomlin followed up to nod the rebound beyond James' despairing dive to give Posh the perfect start.

City's starting line-up showed three changes from the last game, while manager Derek McInnes switched to a 4-4-2 formation with Albert Adomah pushed up alongside Brett Pitman in attack.

Lacking natural width on the right, the visitors looked unbalanced to say the least and struggled to retain possession and mount any sort of sustained pressure during a first-half in which Peterborough demonstrated more of a cutting edge.

If Kalifa Cisse's job was to check Boyd's runs from deep, he was falling short in this department and Peterborough's livewire midfielder was causing more or less constant problems at the head of a diamond shape.

He twice had shots charged down and then set-up David Ball for an angled shot which flew into the side-netting.

Posh should have extended their lead on 27 minutes, only for Ball to shoot weakly at James from 15 yards out with only the former England keeper to beat. Boyd found himself in a similar position moments later when a James miss-kick fell at his feet, but he hesitated and allowedthe keeper to redeem himself with a last-ditch tackle and clearance.

McInnes changed tactics at that point, moving Adomah to his more accustomed position on the right flank and reverting to a 4-5-1 formation which left an isolated Pitman to plow a lone furrow up front. But still the chances continued to materialise for the home side and Gabriel Zakuani met Grant McCann's in-swinging corner with a header that grazed the top of the cross bar.

It took City 37 minutes to threaten the Posh goal. Marvin Elliott got royund the back of the home defence and pulled the ball back for the in-rushing Cisse, whose shot flew woefully high and wide from the edge of the penalty area.

Most of the action was at the other end, however, and James was forced to go full-length to tip over a fierce drive from Tomlin.

Starved of opportunity for 45 minutes, Pitman was finally allowed a sight of goal in time added on at the end of the first half. Richard Foster's long throw was flicked on by Elliott and Pitman's deft flick rolled agonisingly wide of the upright.

Aware that he had to change things at half time, McInnes withdrew Cisse and sent on Chris Wood to partner Pitman at the start of the second period. And the improvement was immediate.

Pitman hooked a shot just wide, Liam Fontaine saw his header saved by Paul Jones and Stephen McManus, rising unchallenged to meet a corner with a powerful header, was denied his first City goal by Lee Frecklington's desperate goalline clearance.

Realising they were in a contest all of a sudden, Peterborough responded in kind and McCann was inches away from a doubling the home side's lead when his long-range drive flashed just wide with James struggling to make his ground.

City fell further behind in the 63rd minute and they only had themselves to blame. It had been apparent for some minutes that McManus had sustained an injury and could not continue. But McInnes opted to leave him on the pitch and he was in no position to prevent Ball skipping past the stricken centre-back's feeble tackle and smashing his shot past the stranded James and into the roof of the net.

McManus was replaced by James Wilson immediately afterwards, but the damage had already been done.

Posh manager Darren Ferguson introduced substitute Emile Sinclair for the final 18 minutes and the striker should have made it 3-0 when somehow side-footing wide of the target from point-blank range.

But Sinclair made amends five minutes from time, supplying the cross from which Tomlin rammed home the third goal from close-range to make sure of victory.

Peterborough (4-4-2): Jones; Alcock, Zakuani, Bennett, Briggs; Frecklington (Tunnicliffe 80), McCann, Boyd, Tonlin; Taylor (Kearns 86), Ball (Sinclair 72).

City (4-4-2): James; Foster, Fontaine, McManus (Wilson 63), McGivern; Elliott, Cisse (Wood 46), Kilkenny (Bolasie 76), Pearson; Adomah, Pitman.

Referee: David Phillips (West Sussex)