The step up in class becomes reality tomorrow for the top two teams in Sussex.
Worthing, fresh from back-to-back promotions, get their first taste of London One when they go to Bishop's Stortford.
It is not quite the real thing for Haywards Heath, but a very good rehearsal as they host Basingstoke in the first round of the Powergen Cup.
The sides will be rivals in Three South when Heath get their first ever National League season under way.
Worthing are accustomed to finishing in the leading places and are targeting a top five spot this season.
They have 31 players unavailable for this opening weekend but former St Mary's flanker Russell Carr gets a debut and Stuart McLachlan returns at No. 10 after a season with Portsmouth.
Coach Ian Davies said: "It's another step up with virtually the same squad we had in division three.
"We need another back to strengthen the squad and, if we do that, top five is not out of the question."
Stortford also went up last year as champions of London Two North.
Several Haywards Heath players picked up a flu bug last weekend when they enjoyed two days of tough training with the new Celtic League outfit Neath-Swansea Ospreys.
Early morning runs, set piece routines, strength and fitness work and team bonding were all on the agenda at the Ospreys'training base in Llandarcy.
It has left skipper Alex Meredith and his men raring to go, despite the sniffles.
Basingstoke were the last away side to win at Whitemans Green, 18 months ago, and Meredith said: "We've got a point to prove.
"'We've improved since we played them in London One and we go into this game full of confidence."
Heath give debuts to flanker Will DeGrauchy, from New Zealand, and former Eastbourne centre Jon Groenen.
Prop Will Bauer, who is on the fringes of the United States international set-up, is on the bench. Both games kick-off at 3pm.
Sussex hold their annual meeting at Burgess Hill RFC next Tuesday evening when they are expected to confirm a new sponsorship deal with Greene-King.
Old Brightonians beat Barns Green 45-15 in their Sussex Plate tie last night
Haywards Heath: Cook, Pymm, Groenen, Stocker, H. Goodburn, Graham, Meredith; Shadbolt, Denslow, Cassidy, Lyall, Ure, DeGrauchy, Rankin, Wattam.
Worthing: Coulson, Kimmer, Butler, Adams, Cruz, S. McLachlan, M. Imrie; Bruce, Alcott, Bennett, Dove, DeBoer, Carr, Cox, Davis.
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