The two remaining second division clubs tumbled out of the Gray Nicolls Cup at the quarter-final stage.
Preston Nomads and Roffey were each beaten comfortably by Premier League opponents on Sunday.
Horsham made 309-9 with Michael Bright leading the way on 113 as Chris Nash hit 41 in support. Mark Jefferson took 3-47. Roffey collapsed to 102 all out as Chris Nash took 3-10 and Bright completed a good day with 3-26.
East Grinstead amassed 266-4 against Preston Nomads as their skipper Alex Edwards finished with 80 not out.
Zimbabwean Richard Sims made 64 and left-hander Neil Turk 54. Nomads were then dismissed for 184 as left-arm spinner Craig Fowle took 5-41.
Eastbourne owed a debt of gratitude to Brighton College youngster Malcolm Waller who made 66 of their 200-4 from 45 overs at Brighton and Hove.
But it proved only academic as the home side reached 203-3 from 39.5 overs to win by seven wickets.
Sussex player Bas Zuiderent led the way with 68 not out and Martin Adams continued his good form with 57.
At Steyning, visitors Hastings struggled somewhat with the bat but, in turn, won the game when they bowled out the home side for just 166 as they chased a target of 204-9.
For Hastings, Richard Jackson led the way with 43 and the home side looked on the way to victory as Mark Fraser hit 44 and skipper Giles Haywood 40.
But the Hastings bowlers had other ideas and three of them grabbed three wickets each.
John Morgan took 3-56, Matt Love 3-26 and George Campbell 3-38.
Results: East Grinstead 266-4, Preston Nomads 184 (David Smith 51, Craig Fowle 5-41); Horsham 309-9 (Michael Bright 113, Chris Nash 41, Mark Jefferson 3-47); Roffey 102; Eastbourne 200-4 (Malcolm Waller 66), Brighton and Hove 203-3 (Bas Zuiderent 68 not out).
Semi-final: Horsham v Brighton and Hove, Hastings v East Grinstead.
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