Teenage skipper Jeremy Green had his first taste of defeat in the premier division as Chichester enjoyed their opening victory of the campaign.
Pakistani right-arm fast bowler Fazl-e-Akbar played a leading role grabbing 4-45 as Steyning were dismissed for 140.
Green, 19, probably the youngest player to regularly captain a Sussex League side, hit 53.
The hosts scraped home on 141-8 with Daniel Oliver (43) and Fazal (39) top scoring as Sussex's Jason Voros (4-36) and Green (4-39) made inroads.
Green said: "I am enjoying the challenge of captaincy and it brings out the best in my game.
"I now have to make sure I start to bring out the best in others.
"Our seam bowling is much better than last year and we are hoping that the leg-spin of Conrad Mumby will start to get us wickets.
"We really should have won against Chichester.
"We had them 20-5 and let them off the hook."
The new leaders are Brighton and Hove, who have an 11-point advantage over Horsham after both earned their second victories of the season.
Brighton had a comfortable six-wicket win at Three Bridges and Horsham won by 69 runs at St James.
Three Bridges were dismissed for 111 with Andy Cornford (5-27) on song. Stephen Ades (37 not out) and skipper Patrick Spencer (30 not out) steered Brighton home in a fifth-wicket stand.
Sussex's Carl Hopkinson (44) starred in Horsham's win as they made 199 all out (Stephen Green 3-25).
Hopkinson took 7-39 as the hosts tumbled to 130 all out. Ed McGregor (64) top scored.
East Grinstead had a massive 167-run win over newly-promoted Lewes Priory.
Grinstead's Paul Turk (66) and James Atkin (66 not out) helped them to 237-9 (Sher Khanaga 4-48) before Lewes fell for 70 (Duncan Shoebridge 4-12).
Lewes skipper Michael Murray, still looking for his first win, said: "We paid the penalty for dropping too many catches.
"We then batted as badly as I can remember, there were far too many loose shots.
"We will have to go back to the drawing board or it is going to be a long and fruitless season."
Last year's champions Hastings were frustrated by Eastbourne after allowing them 61 overs to chase their score of 251-4 declared in which Johnny McLean hit 102. Eastbourne reached 216-8 at stumps with Sean Heather (44) top scoring.
Cuckfield and Littlehampton, who both narrowly missed promotion last season, are separated by a single point at the top of division two.
Visitors Bexhill declared at 184-5 (Jeff Topp 58) as Tim Mole took 5-58 for Cuckfield.
The young Piolet brothers, Stefan (74 not out) Christian (40 not out), helped steer Cuckfield to a three-wicket victory at 185-3 with an unbroken fourth wicket stand. Turnbull took 3-67.
Hosts Littlehampton beat Stirlands by 41 runs after being dismissed for 146 (Carl Stedman 41), Australian Steve Adsmill returning 6-38.
The visitors then crashed to 105 all out as Steve Hunt and Adam Tester took three wickets apiece.
Roffey beat Worthing, who were restricted to 189 as Mike Norris (5-39) did the damage.
Norris struck 75 as Roffey made 193-8 (Matt Poole 5-33).
Preston Nomads trounced Pulborough by 108 runs after posting 208-3 declared with Steve Gatting (67), Hugo Shephard (49) and skipper Will Davis (40 not out) on song. Pulborough were dismissed for 100 (Kashif Ibrahim 5-25).
Sidley enjoyed a comfortable eight-wicket triumph at home to a weakened Haywards Heath side.
Heath made 177-9 (Andy Grenville 45) as swing expert Peter King (4-65) led the bowling attack.
Jonathan Haffenden (70) and new overseas signing Nasir Hameed (47) led the successful run chase.
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