Roffey suffered their maiden defeat of the campaign and as a result slipped off the top of the Premier Division table.
A 72-run loss at the hands of fellow title chasers Cuckfield meant it was all change in the top half of the table.
East Grinstead took pole position and lead second-placed Cuckfield by 16 points, with Roffey a point further back in third.
A starring show from Cuckfield opener Joe Ludlow saw him blast 117 not out to help the home side to 215-9 in their 58 overs.
A disappointing day then saw Roffey slump to 143 all out inside 47 overs.
Boars skipper Matt Davies said: “Getting Jeet Raval early was a big wicket, but we just didn’t bowl well enough on a pitch that should’ve suited our bowling attack.
“Joe Ludlow batted well but I think we could’ve bowled a lot better at him.
“In reply, they bowled reasonably well and we batted poorly, there’s not much more I can really say.
“It’s still early days and a lot of big games are coming up for the top sides.”
Spinner Rohit Jagota quickly found turn and bounce, having overseas Jeet Raval caught behind, then Dominic Sear (one) followed soon after, caught at short leg.
Roffey quickly began attempting to tie down Cuckfield, but the medium pace of George Fleming (3-28) trapped keeper Brad Gayler lbw for six.
Harry Clark and Ludlow quickly began upping the score to 81 before Clark (22) edged the returning Jagota.
Ludlow remained the constant throughout the Cuckfield innings and he put on 80 with Abi Sakande (33), before the latter ran at Fleming to find himself stumped.
Ludlow finished on 117 off 171 balls, having looked rarely in trouble on an extremely challenging batting surface, on which no other batsman scored more than 33 as they finished on 215. Luke Barnard claimed 3-90.
Cuckfield bowlers Josh Hayward and Sakande (4-28) then made scoring difficult. The latter’s pace saw off Josh Fleming (five) - caught in the slips attempting to avoid a bouncer - before Chris Webb (one) was caught behind.
Jibran Khan (31) quickly began to counter, but he could only look on as Theo Rivers (17) was caught behind and the dangerous Jagota (one) followed.
Despite a promising resistance from Usman Khan (24) and Ben Manent (33), both fell playing rash shots.
Nick Patterson (4-28) returned to take two more wickets, and although the Roffey tail took the game deep, they finished all out for 143.