Crystal Palace scored two second-half goals to knock out Championship rivals Southampton and book their place in the Carling Cup quarter-final.
Second-tier leaders Saints had the best chance of the opening half when Jonathan Forte forced Palace keeper Lewis Price into a smart save.
But Darren Ambrose put Palace in front in the second half when he slotted home from a cross by Jonathan Williams.
Jermaine Easter then scored a penalty after Dan Harding fouled Williams.
Saints boss Nigel Adkins made 10 changes to his line-up from the weekend's draw against Reading and, despite an impressive debut from 16-year-old James Ward-Prowse, the reshuffled side came up just short against a Palace side that also featured several fringe players.
Indeed it was a highly rated Palace youngster, Jonathan Williams, one of seven changes for the hosts, who proved the difference with a part in both goals.
It could have been very different, though, had Saints midfielder Jack Cork's header not been cleared off the line by Stuart O'Keefe in the opening minute.
Palace were restricted to long-range efforts in the first half, none of which came close to troubling Bartosz Bialkowski in the Saints goal.
After the break Palace striker Easter fashioned a decent chance for himself when he burst past Cork and reached the edge of the area, but once again the finish did not match the build-up.
Easter should have broken the deadlock 15 minutes into the second half when Williams and Ambrose combined to tee him up just inside the box, but this time the striker dragged his shot wide.
It looked as if it would require something magical or calamitous to break the deadlock, and it was the latter that finally did the trick as a sliced clearance from Aaron Martin allowed teenager Williams to get round the back of the Saints defence and cross for Ambrose to finish.
Rickie Lambert and Guly do Prado were summoned from the bench, but the visitors' luck was out. Harding's trip on Williams sent the midfielder tumbling in the area and Easter scored from the penalty spot to send Palace through to the quarter-finals for the first time in eight years.
Crystal Palace manager Dougie Freedman:
"We are pleased, it was a hard-fought win, we had to defend for most of the game.
"We gave a lot of respect to Southampton, who are a very good team. But we defended well and that enabled us to go on and get the goals.
"Over the 90 minutes we deserved to win."
Southampton manager Nigel Adkins:
"We came with the mentality to win the game even though we made 10 changes.
"Ultimately it's about winning and we haven't. But we are totally committed to the youth system at Southampton and I'm delighted with James Ward-Prowse, helooked very assured and comfortable with the ball.
"We've utilised this competition to give the youngsters an opportunity. It's a hard one as a manager, it's about having a squad and utilising it well. The players need game time."