Flixton will join champions Hull Zingari in the Premier Division next season after they secured promotion ahead of long-time rivals Sewerby.
The pair had been locked together in recent weeks but a second consecutive defeat for Sewerby, saw the pair finally separated.
The runners-up spot was secured by Flixton with a dominant performance over a visiting Harrogate side which was bowled out for 119 with Connor Stephenson taking 5-27, Harry Walmsley 2-15 and Tom Norman 2-11, only Jordan Marshall making any impression with the bat scoring 34.
The hosts eased to their target inside 22 overs with Richard Malthouse (41no) and Will Norman (38no) remaining unbeaten.
Sewerby’s promotion challenge ended in extraordinary circumstances when they lost by two wickets at Heworth.
Scott Cooper was the leading runscorer in the match with 27 as Martin Boothroyd (4-21) and Steve Lawrence (3-34) combined to dismiss the visitors for just 93, but the game proved to be far from over with skipper Aidy Long taking 4-13 as the home side found batting equally challenging finishing eight down by the time they reached the target.
In Division Two Ebor, Scarborough 2nds eased to a seven-wicket triumph at Acomb 2nds.
Matthew Graves took 4-28 and Kristian Wilkinson 3-39 as the hosts were dismissed for 197 in 43 overs, Joseph Burton leading the way with a fine 72, assisted by Alex Topham (32) and Harry Watkinson (28no).
Matthew Watson laid the foundations of a successful reply, Wilkinson capping a fine day with 34 not out, but it was the big-hitting James Bryant who was the main man with the bat, smashing an unbeaten 84 to guide Scarborough to victory off only 33.1 overs.
Bridlington claimed the bulk of the points in their winning draw at home to Pickering 2nds, John Major's unbeaten 74 the leading light for the hosts.
Frankie Reffold also weighed in with 44 as Brid posted 205-5 from their 45 overs, Mark Shepherd bagging 3-47.
In reply, the Pikes battled away with fine knocks from Ryan Taylor (44), Ryan Boyes (40), Joe Harland (31) and Shaun Smith (27) helping them hang on for a losing draw on 182-9, Harry Burton the top Brid bowler with 4-63.