Alan Thompson’s Blues youngsters found themselves a goal down after just seven minutes at the Brakes’ New Windmill Ground.
The hosts struck twice more, before Liam Truslove found the back of the net for the visitors with eight minutes to go.
Despite the loss, U21s coach Thompson felt it was a good workout for his side, which contained no less than four trialists in the starting XI.
“In the first-half the pitch was dry and bobbly which made things difficult, but in the second-half the heavens opened and we started moving the ball around a lot better and looked like good players again.
“Leamington didn’t create an awful lot and it was defensive errors and a lack of concentration on our part which cost us the goals
“We did manage to create some chances, but their goalie made three or four decent saves.
“On the whole we struggled to cope with the physicality of them because we were a young group. But it was a good test because you get to learn a lot about them if they can stand up to it and cope with the physical side of the game.”
* Blues U21s won their opening pre-season game against Worcester City 3-0 at the weekend in a behind-closed-doors fixture at Wast Hills. Koby Arthur was on target twice, with George McGee notching the other goal.