Wearing all yellow, it was Alex Inglethorpe's side that was pretty much holding sway in the opening exchanges on a cold South Coast evening and Danny Rose came closest to putting an early marker on the occasion with a drilled shot that skidded just wide. Rose was positioned just off the front at the start - although there was significant manoeuvre as the first half progressed - along with Dean Parrett, behind striker Olsen.
Saints came close to profiting from a goalmouth scramble following a corner in the 12th minute, Matthew Patterson managing to shoot on the turn, but blocks were quickly applied in numbers. Calum McNish then tried his luck from roughly 20 yards, while failing to give goalkeeper Jamie Butler his first work of the evening.
Moments later a free-kick executed with considerable poise by David Hutton rattled the crossbar before Patterson did warm the hands of Butler with a effort that zipped across the surface at the other end.
Andrey Pernecky in the home goal displayed superb reactions to deny Parrett an entry on the scoresheet, albeit that it would have been via a slight deflection. Hutton, who was responsible for injecting moments of quality into what became a scrappy period leading up to the half hour mark, ensured parity was restored with a goalline clearance after Butler had taken the sting out of a thumping effort from Joseph Mills.
The home side should perhaps have secured a lead just ahead of the break when Kayne McLaggom forced Butler into a smart stop but the ball ran loose and McNish looked set to provide his side with the advantage from around penalty spot distance. It took a brave and perfectly timed block from central defender Callum Butcher to prevent such an outcome.
Yuri Berchiche flashed a free-kick just wide as a crisp tempo was set in the second half. Jake Livermore then bustled a path through to goal and it took a obstruction in the shape of Jeffrey Imudia to stop him in his tracks.
The deadlock was broken on the hour, the key being a sublime defence-splitting ball from Rose that set the speedy Olsen on the charge. Pernecky advanced and pulled off a great save, but the ball bounced back into the shins of Olsen and rolled into the net. Cue somersault celebration from the Norwegian.
Matters took a further turn for the worse for Saints minutes later when Imudia was dismissed for a second yellow following a crude challenge on Parrett, having earlier been cautioned for a foul on Rose.
Livermore picked out the run of Olsen with the same end result of the ball ending in the back of the net, but this time a very late flag raise by the assistant curtailed the joy. Skipper Livermore was finding his range and his dissecting passing presented Rose with an opportunity that could well have extended the lead. Livermore later stung the fingers of Pernecky with a rasping drive that the goalkeeper managed to claw away from the top corner.
Saints attempted to rally but were comfortably repelled until the whistle sounded to signal was, in fact, the first victory this club has recorded at the St Mary's Stadium.
A second half goal from Alex Olsen secured a route through to the fourth round of the FA Youth Cup at the expense of Southampton.It was a close run thing at St Mary's but Olsen's goal, swiftly followed by the home side suffering a reduction in numbers due to a second yellow card, proved too much to overcome and now we play the winners out of York and Chester.