The defeat was the first time that United had failed to pick up maximum points on the seasons opener since a 1-1 draw with Midhurst & Easebourne in 2011.
It was a much changed United side that took to the field, with six players handed their first competitive starts by Simon Rowland. Callum Christie, Ryan Cooper, Toby Clifford, Dom Clarke, Seb Saunders and Alex Howell all made their Oval bow in the fixture, with a further new signing Slav Stoyanov taking his place on the substitutes bench.
It would be two of the debutants who would link up for the first talking point of the contest as Saunders powered his way down the left channel before cutting back for Howell, who went to ground inside the penalty area. No penalty was awarded as Howell found himself in the referee's notebook for simulation.
With the exception of Howell's caution, the first half hour was largely uneventful as both sides struggled to take any sort of stranglehold of the contest in warm conditions on a glorious summers day.
Somewhat against the run of play, it was the visitors who took the lead as a long throw was flicked on to last seasons top scorer in the SCFL, George Landais, who cushioned a header across the helpless Christie.
Four minutes later, United were back on level terms as Dom Clarke pounced on a short free kick that was awarded after the burly striker was adjudged to have handled the ball as he dispossessed Mitchell Hand to slot past Luke Hutchins in the visitors goal for his first goal since his summer move from Eastbourne Town.
The games turning point came on the hour mark as Saunders won the ball on the right wing and drove at goal, before crossing for Clarke who just failed to connect with the ball.
Almost immediately, Littlehampton attacked and the ball fell to Landais, who opened his body to curl an unstoppable effort into the far corner off the underside of the bar past the stranded Christie.
Littlehampton made the game complete with a little over fifteen minutes remaining as substitute Rob Hutchins shrugged off the advances of Peter Featherstone to calmly slot past Christie and ensured the three points returned to West Sussex.