Jan Poortvliet was forced to reshuffle his defence with Svensson worryingly out injured with pain in his troublesome knee after a below par performance against Blackpool that suggested all was not well.
Curiously, the Dutchman selected two teenagers Cork and Lancashire at centre back ahead of the experience of Perry, experience that was sorely missed with Saints guilty of some naive defending, badly missing a leader at the back.
It was summed up by a terrible goal to concede after just thirty seconds with a scuffed header from Lancashire bouncing through to Blackstock one of two QPR men inexplicably in acres of space within a few yards of the goal.
Lancashire's enthusiasm got the better of him with a scything challenge on Delaney to earn a straight red after just 31 minutes. He may have got away with a yellow on another day, but it was a naive challenge.
The reshuffle actually improved Saints at the back with Wotton providing some much needed leadership, even if he was lucky to avoid a red when his studs went over the top of the ball and into Parejo's leg.
The experiment of playing midfielders at full back continued, but Surman and James had little chance to go forward negating their potential impact and not helping things at the back.
Midfield saw some neat interplay of passes with Lallana at the heart of Saints' best moves, despite being moved to the right to accommodate Schneiderlin in a more advanced and arguably less effective position.
However, as a group they failed to protect their defence with Gillett and Schneiderlin frequently caught up field leading to a flurry of QPR chances that should have seen them out of sight by half time, but for the heroics of Kelvin Davis.
Up front McGoldrick had a low key afternoon on a day when Saints may have benefited from Stern John's hold up play and experience.
Verdict
After a two week break, Saints failed to learn the lessons from the Blackpool defeat with some suicidal defending, summed up by the opening goal but repeated as Blackstock ran riot against his former club.
Of course the youngsters had their share of bad luck. A comedy opening goal to put them on the back foot, the injury to Holmes, a red that could have been a yellow and a clearly offside second QPR goal, but that glosses over the failings in defence.
They deserve huge credit for fighting their way back into the game thanks to a sublime goal from Lallana that will have the Premiership vultures circling, but in truth QPR could and perhaps should have scored more than four.
The talk of getting the right blend of youth and experience was belied by a very inexperienced line-up, again summed up by Lancashire's moment of madness a mere half hour into his league debut.
Saints are capable of playing some wonderful football, but unless they learn to defend they are going to get picked off time and time again, with the side badly lacking the discipline to reorganise when their free flowing attacks broke down.
Time after time simple balls over the top or into the box caused panic undoing much that was to admire in Saints' pass and move style. After equalising Saints needed the experience to balance defence with ten men against attack at all times. Sometimes a point is enough a man down.
Unfortunately, Saints have little time to prepare for the next game with big-spending Ipswich the visitors on Wednesday. Unless the youngsters learn quickly the art of defending as a unit, it could be a painful few weeks in the relegation zone. Otherwise Svensson's knee could once again be Saints' downfall.