A much changed Casuals line-up gave a good showing but the visitors proved too effective in the final third.
Elvis Hammond opened the scoring in the 7th minute and Nathanial Pinney doubled the lead with a deft lob after 26 minutes.
The home side gave as good as they got in the second half but Pinney blasted home his second and the K's 3rd with 6 minutes remaining.
All the best to Kingstonian in the next round and also for the remainder of the season.
Tonights other results involving Ryman South sides.
Carshalton Athletic 1 v 1 Whyteleafe
Whyteleafe won 4-2 on penalties
East Grinstead Town 4 v 2 Three Bridges
Margate 2 v 0 Hythe Town
Ramsgate 1 v 1 Folkestone Invicta
Ramsgate won 4-3 on penalties
Redhill 1 v 3 Burgess Hill Town
Sittingbourne 0 v 1 Faversham Town
South Park 0 v 2 Leatherhead
Tooting & Mitcham Utd 0 v 5 Merstham
Walton Casuals 2 v 1 Chipstead
Whitstable Town 1 v 2 Herne Bay