Lakeside led 2-0 at the break with goals from Alex Cox and Brandon Jefferis, but Plympton really pushed the hosts hard in the second period.
The visitors pulled a goal back five minutes after the break and there were plenty of chances second half at both ends of the field.
But Lakeside held on to claim the win that leaves them second in the four-team west regional pool, three points behind Plymouth Argyle Development, who they play next week.
Swipe to see full gallery. All pictures are low resolution and are protected by copyright.