Manager Tony Vance says a 5-2 loss for Guernsey FC at Tooting and Mitcham was an "awful night" for his side.
Vance, who had 19 players unavailable, saw his side go a goal behind after 10 minutes and they trailed 2-0 at half-time before Luke Winch got one back.
Guernsey conceded early in the second half and were 5-1 down after 75 minutes before Marc McGrath's late consolation.
"It was an awful night for us," Vance told BBC Guernsey after what was their third-worst defeat in club history.
The defeat saw Guernsey, who have won just one of their last seven league games. drop to 14th in the Isthmian League Division One South.
|Guernsey FC's recent poor league form|
|16 September: Faversham Town (a) Lost 3-0|
|20 September: Folkestone Invicta (h) Drew 0-0|
|24 September: Ramsgate (h) Drew 1-1|
|27 September: Horsham (a) Won 4-2|
|4 October: Burgess Hill Town (h) Lost 2-0|
|11 October: Hastings United (a) Lost 4-1|
|21 October: Tooting and Mitcham United (a) Lost 5-2|
In Guernsey's four-year history, their only heavier defeats in competitive games came last season when they lost 6-2 away at Horsham and 4-0 at Walton and Hersham.
"People have got to appreciate that, when you're changing it all the time, different personnel are playing with different people every time and it's quite hard," Vance added. "But we weren't good enough today."
Despite only making three changes to his starting line-up from Saturday's FA Trophy win over Barton Rovers, Vance says injuries and work commitments to his players meant his options were limited.
"Up until Monday morning I only had 10 players, but I managed to scramble 14 for tonight," he added. "I must have the most unique job in football and the most unique club in football.
"We've got a completely different back four, positional changes and a completely different goalkeeper. How many teams do that every game?
"I don't think I've had a settled side and that's the way it goes. I've said time and time again that when we get our strongest group available we're a match for anyone."