Two goals inside the first 13 minutes from Ashton Leigh put second tier Meon in control at Furze Lane.
Louie Jeff and Shane Cornish pulled Cosmos level before Meon's Max Davies hit the bar twice towards the end of the first half.
The second period was all Meon, with Cosmos pinned back for the majority of the half but defending well and restricting Meon to shots from outside the box.
But with two minutes remaining, Cornish scored the winner with Cosmos’ only shot on goal in the half.
Perri King was awarded man of the match for his heroics in the Cosmos goal.
In the only CoPSL Division 2 fixture, Cosham Trades joined The Meon on 18 points - three behind leaders Southsea with both teams having a game in hand - thanks to a 7-2 drubbing of Old Boys Athletic. Morgan Easen led the spree with a hat-trick with Roberts Grudinskis and Liam Tieney also among the goals.
Jubilee leapt to the top of the Division 3 table with a 2-0 victory over Bransbury Wanderers, George Cartmell and Liam Young on target.
Hot on their heels are Mother Shipton, who defeated North End Lions 3-1 with David O'Donnell, Stephen Ledger and Frankie Kemp on target. Shipton remain three points behind the leaders but have four games in hand.
Cross Keys Athletic gained a valuable point at the bottom of the division after a 1-1 draw with Waterlooville Wanderers. Steve Moss netted for the Keys with Ryan King replying.
Prince of Wales lead the way in Division 4 by five points. But it could have been eight if they hadn't have dropped three in their double banker with Sheperds Crook.
The first game went to plan as Glyn Cooper, Louis North and Lee Tigwell scored for PoW in a 3-2 win. But the second game saw Crook triumph 3-2.
Archie Drury (3), Farren Jervis and Ty Moody gave second-placed AFC Solent a 5-1 success against Jubilee Reserves.
Fleur De Lys were made to fight all the way for their 3-2 win over bottom club Co-Op Dragons. Dragons were level thanks to goals from Simon Longhurst and Russ Oastler, but FDL triumphed through Ben Winslade, Harry Beckingham and Harry Bamber.
Connor Jepson (3), Maurel Inamba (2) and Charlie Ruffell (2) led the Lakeside Refit spree in their 10-2 thrashing of Friends Fighting Cancer.
Michael Anslow scored a brace as Watersedge Park defeated Bedhampton Village Reserves 5-2.
Freehouse A preserved their 100 per cent record at the top of Division 5 with a 6-1 spanking of Saturn Royale. Jason Shewsbury led the half-dozen haul with a hat-trick with Chris Thompson, Scott Thompson and Edi Domingos also netting. Kyle Ward replied.
Afc Fairfields and ACFC moved closer to safety after their 1-1 draw. Fairfield dominated the first half and were rewarded with a goal from their keeper, but the second half was all AC's and they levelled through Dominic Calvert. AC should have gained all three points but hit the bar and post and missed a couple of sitters in the second half.
Sub Spencer Baldry scored twice for second-placed Padnell Rovers in a 3-0 Division 6 victory against Freehouse B, Jamie Labrow also on target.
Top scorers of the day were Pelham Arms, who trounced Spartan Athletic 12-1 with Liam Shepherd netting five times. There was also a hat-trick for Alfie Robinson and two each from Malcy Ferret and Albert Gauntlett. Jamie Robinson replied.
Third placed Hatton Rovers (Liam Karim) drew 1-1 with Milton Park Rangers (Mitchell Smith).
Compiled by Paul Oastler