On a wet afternoon at Inver Park, Larne were sluggish out of the blocks after their return from midweek European action.
However, Andy Ryan did force an excellent save from Patrick Grogan after a quarter of an hour.
And just after that chance, the ball was in the net at the other end as Leo Alves' excellent work down the right found Steven Scott who cut back to Knowles, and he steered first-time into the bottom corner.
The next big chance of the half fell to the Swifts again as Alves tested Rohan Ferguson from the edge of the box with the Scottish stopper at full stretch to tip around the post.
There were penalty appeals at both ends waved away before the break as Knowles and Ryan both hit the deck.
The home crowd were begging for more from their side in the second half but, in truth, it never really came.
Any chances they had were of the half-chance variety with another good Grogan save from a Sam Todd header the best they could muster.
Meanwhile, the Swifts were in scintillating form and, after Alves robbed Todd in his own half, he fed McGovern, who picked out the top corner from all of 25 yards to make it two.
There was another blow for Larne when, barely two minutes after coming on as a substitute, Aaron Donnelly limped off.
With the home support at Inver Park already frustrated, the Swifts added a third with five minutes remaining when Glenny headed home Alves' corner.