Sussex academy director Keith Greenfield top scored for Brighton and Hove but it was not enough to prevent the title challengers from tumbling to a 14-run defeat.
Greenfield hit 56 not out but Littlehampton's mixture of swing and spin proved decisive as second-placed Brighton were dismissed for 151.
Young pace man Luke Vinter and left arm spinner Chris Hanks each took 4-36.
The visitors were chasing a Littlehampton total of 165 all out which included 87 not out by Chris Cooke.
The exciting Preston Nomads team went to The Saffrons and beat Eastbourne by just five runs as the last wicket fell in the final scheduled over.
After being put in, Nomads never found runs easy against Sussex academy spinners Ollie Rayner (4-67) and Tom Smith (3-36) and the declaration came at 193-8.
Joe Gatting led the way with 69, wicketkeeper Jack Willow made 33 not out and Steve Gatting 28.
Eastbourne then made 188 all out with Smith scoring 37 and Jack Hepburn 33. Among the wickets for Nomads were Carl Simon (3-52), Nick Hobbs (3-56) and Steve Rigg (3-33).
Leaders Chichester won by 66 runs at home to Hastings. Jez Goode made 74 in Chi's 225-6 before Pakistani paceman Fazal-e-Akbar took 5-45 as the visitors were bowled out for 159.
East Grinstead looked to have modelled their batting on the Lashings' Twenty20 technique that was demonstrated at their ground against Sussex last Tuesday as they took on Horsham.
They slumped to 30-3 but Simon Williamson, on his league debut for the club, then cracked 110 after being dropped at cover on nought and Paul Turk made 66.
They were finally dismissed for 260 in just 48.3 overs, Phil Hudson taking 5-45 and Chris Nash 4-73.
Horsham were left 61 overs to reach that target and looked well on course as Nash hit 67, Will Howard 52 and Luke Marshall 35.
However, Turk (3-15), Craig Fowle (3-34) and Alex Edwards (3-57) caused problems and Horsham were forced to hang on at 217-9 at the close.
Steyning, put in by Three Bridges, took maximum batting points with a total of 254-4 declared as Jibran Khan hit 79 not out against his former club. Rob Wakeford added 46, skipper Jeremy Green 44 and Wayne Spiller 42.
Three Bridges failed to mount a serious victory bid and reached 230-6 at stumps. One-time Sussex opener Jerry Heath made 63 and Nick Creed 53 not out while Steyning off-spinner Dave Mates claimed 3-81.
Cuckfield went top of division two after beating Bexhill by nine wickets.
Bexhill reached 161 all out after being put in by the hosts. Jesse Lewis struck 85 as Nick Patterson (4-50) and Andy Emtraj (4-60) ripped in.
Skipper Chris Mole then cracked 84 and teenager Stefan Piolet added 55 not out as Cuckfield coasted to victory.
With Worthing not in action, St James's Montefiore went second after an impressive home win against Roffey.
Sam Chettlebrough struck 132, gaining support from Ed Hart (32 not out), as St James posted 207-5 declared, with Rob Nevins' 3-88 being the pick of the bowling.
Simon Schivnarain struck 43 in reply but Roffey were bowled out for 167 with Zeuben Bhettay (5-37) and Kris Johnson (4-46) doing the damage.
Stirlands won for the second week in succession as they beat Lewes Priory by six wickets.
Visitors Priory decided to bat but were restricted to 176-8 declared, skipper Michael Murray scoring 54 not out as Paul Dorkings took 4-36.
David Briance then cracked 73 not out for Stirlands, including a match winning six, to lead his team to victory. Tyrone Lynch was the pick of the Lewes bowlers with 2-44.
The remaining game was a draw at Sidley as visiting Pulborough, still without a win so far, turned in probably their best performance to date.
Pulborough reached 207-7 declared with Ashley Clarke making 46 and Jodie Healey 44.
Pete King (39) and Chris Hunnisett (35 not out) gave Sidley a chance but, in the end, they held on at 166-7.
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