Guernsey FC were edged out in an 11-goal thriller by League Two AFC Wimbledon as they lost their their first ever game 6-5 at Footes Lane.
The friendly was the first of three planned warm-up matches as the club prepare for their first season in the Combined Counties League.
Captain Sam Cochrane said: "I thought we played some very good football. This challenge is what Guernsey needs."
Guernsey's next game is on 23 July at Footes Lane against a Bristol City XI.
A crowd of 1,060 turned out for the clash with the former Combined Counties League side, who won promotion from the Blue Square Bet Premier last season.
The Green Lions took the lead in 10th minute when Ryan Zico Black converted a free-kick into the top left corner past Jack Turner.
It was the only time Guernsey were ahead as they found themselves 3-1 down at half-time after goals from Jake Rose, Jerson Dos Santos and Zac Richards.
As the second half continued at a frentic pace the hosts created a number of chances but the Dons made it 4-1 through Dos Santos's second.
Then came four goals in seven minutes as Ross Allen pulled a goal back before Brendan Keirnan regained AFC Wimbledon's three-goal cushion.
Captain Sam Cochrane and Tom Strawbridge brought the Green Lions' deficit back to just one goal but Cherno Mendy then added a sixth for the visitors with 20 minutes left. Allen powered home his second late on.
The Green Lions' first league game in the Combined Counties League Division One is against Knaphill on 6 August at Footes Lane.