The man who missed the ensuing penalty two days earlier, Luka Milivojevic, scored a cathartic victor with a deft 20-yard curler as Southampton's nosedive towards the relegation zone continued.
Their visitors had instead enjoyed an encouraging run that had significantly strengthened their hopes of survival, but at a demanding time were left at a disadvantage by Southampton entering only their second game in seven days.
The transfer window has officially swung open, and Southampton are looking to dip their toes into the often treacherous January waters, and with teams knowing Mauricio Pellegrino will have money to spend - they could be held at ransom when targeting reinforcements.
Without a goal since February, the pressure had been on lone striker Long to deliver and, with 17 minutes on the clock, he finally found the back of the net.
Crystal Palace fought back from a goal down to win 2-1 away at Southampton.
Palace have recently secured draws from losing positions against Bournemouth and West Ham, and victories over Watford and Stoke.