Just before the hour, Palace were rewarded for their persistence. On a swift counter, Angibeaud slipped a precise pass through to Casey, who fired into the roof of the net – the striker’s 13th goal in nine games.
The young Eagles continued to dominate possession and probe the Southampton defence. On 68 minutes, the ball fell kindly for Sean Somade, who slotted home from close range to put the game beyond doubt.
After Euan Danaher shot high over the bar from a tight angle, Alonso introduced Oduro and Martin in an attempt to freshen things up. However, the Saints halved the deficit thanks to Luke Hawe’s cushioned volley with ten minutes until time.
Palace responded immediately, with Angibeaud heading down into the ground to force a stunning reaction save from Abbotson, keeping the visitors in check.
In the dying embers, Southampton piled on the pressure. Gathercole attempted to bend one into the bottom-right corner but was denied by Mason’s excellent fingertip save, while Thierry Rohart-Brown’s audacious dipping effort from 35 yards forced Mason into a frantic backtrack – fortunately, it sailed the wrong side of the post.
Five minutes of additional time were indicated, and the intensity remained high. The action was end-to-end, with both sides calling their 'keepers into action, though all the stops were routine.
The result keeps Palace top of the U18 Premier League South with 21 points, although their nearest challengers boast several games in hand. Next up for Alonso’s side is the highly anticipated third-round tie against Bradford City at Selhurst Park on Friday, 5th December (18:00 GMT).