Kingston’s first team lost 2-1 due to an own goal late on against Brighton’s second team at Tolworth Court on Wednesday.
With two minutes left on the clock, centre midfielder Knut André Vold, 21, headed the ball in own goal in a failed attempt to block a shot.
Goalkeeper Tom Gurney watched the header slip past his fingers, securing Brighton the win and leaving Kingston devastated after losing their place in the South Eastern Conference Cup.
The teams matched each other throughout the game, which at times was quite heated, despite Brighton being two divisions above Kingston in the league.
KU captain Gareth Chendlik 21, said: “we were the superior team, even though they’re two divisions above us.”
He said: “We knew we would be better as we should play two or three leagues higher than we are now.
“We’re clearly a more well-rounded team than them; they just got lucky with their goals.”
The teams followed each other for most of the match with both scoring early goals in the first half.
Brighton’s Nathan Desnoes was the first to score, after the referee argued with the linesman whether the player was offside or not, resulting in the referee overruling the claim.
After the goal Kingston appeared to be back in the game and were awarded a penalty after a late challenge.
Chendlik took the shot from the penalty spot and aimed for the right corner.
Brighton’s goalkeeper went right but missed the ball and the teams were equal at 1-1.
Brighton’s coach got several warnings for arguing loudly with the referee and stepping onto the playing field.
Due to the massive amount of rain before the game, the players were struggling to stay on their feet on the muddy ground, and a tackle from Brighton left KU’s Conor Billington on the ground clutching his leg.
The game was stopped and Billington eventually had to leave the field and change places with substitute Chris Churchett.
Centre midfielder Sam Bristow said: “Everyone was clearly knackered and you could see people struggled with tired legs.”
Kingston was in the driver’s seat for most of second half and had several opportunities to take the lead but failed to score, much because of excellent play from Brighton’s goalkeeper.
The home team was awarded a second penalty in the 56th minute after Brighton was punished for what appeared to be a handball.
Team captain Chendlik stepped up again after the success in the first half, but Brighton’s keeper was on to him and had no trouble keeping the ball out of the goal.
Bristow said: “In my opinion our level of play was equal, if not better.”
Kingston football’s first team made into the 16 best teams but are now forced to watch the rest of the matches from the sideline as today’s loss means they are now out of this year’s cup.
Chendlik said: “Everyone’s devastated but we need to take this performance into the league and make sure there are no mistakes there.
“Brighton’s leaving here thinking they’re the more effective team and it’s really annoying.”