Manager Garry Monk will have hoped for some of his fringe players to advance their claim for first-team football, but found his men wanting as the hosts helped themselves to a morale-boosting triumph just over a week before the Football League season begins.
Marc Pugh scored twice before the break at the Goldsands Stadium and Brett Pitman added another from the penalty spot in the second half.
Swansea's consolation came in the last quarter of the game courtesy of new signing Jefferson Montero, who grabbed his first goal for the club.
The home side took the lead in the 28th minute as Pugh headed home from Simon Francis' cross before the 27-year-old struck again on the stroke of half-time with a low 18-yard drive that beat the diving Gerhard Tremmel.
Things got worse for Swansea seven minutes after the break when Angel Rangel was penalised for a handball in the area, with Pitman converting the subsequent penalty.
Swansea reduced the deficit in the 68th minute as Ecuador winger Montero's deflected effort wrong-footed Benjamin Buchel and nestled in the back of the net.
Monk is likely to name a stronger line-up for Saturday's match at Bournemouth's second-tier rivals Reading.