Walters smacked in a fine left-footed shot on 11 minutes to put the hosts in front, and just before half-time a powerful volley from the left foot of midfielder Matty Dawson doubled Seamer’s lead.
Sleights pulled a goal back after the interval, but man of the match Walters restored the two-goal lead with a fine finish after beating the keeper to the ball.
The visitors reduced the deficit once again but Seamer held on for the three points that secured the title.
Seamer Sports Reserves chief Gary Dixon said: “We had a few lads missed today with knocks, but we have only lost once in the league all season and all the lads have played very well to win the title.”
Seamer were presented with the league shield by Ken Keld after the match as news filtered through of Falsgrave’s 3-2 loss at Cayton Reserves.
Isaac Sands opened the scoring for Cayton with a powerful shot following a one-two with his brother Jake.
Lewis Short levelled for the hosts, but Jake Sands restored the lead for Cayton after the interval with a clinical finish after a goalmouth scramble.
Man of the match Jon Read, who was excellent in central midfield, smashed in a shot from 35 yards to seal the win for the visitors, although Mikey Anderson did pull a goal back for the home side.
Star man for the hosts was centre-forward Mark Reddy, while keeper Ryan Goodworth also pulled off several fine saves.
Jake, Josh and Isaac Sands also played very well for Cayton.
The battle for the runners-up spot - and promotion - will now go down to the wire, with Falsgrave entertaining Ayton Reserves on Saturday April 4 and Cayton finishing their season at champions Seamer Sports Reserves a week later, on Saturday April 11. Both teams have 40 points but Falsgrave have a better goal difference by seven.
A Sam Mahoney hat-trick sent Tennyson to a 5-2 win at Commercial.
Mahoney’s first goal was a cracking overhead effort, with Rich Tolliday and Adrian Kwiatkowski also on target for the victors. Dan Marston was man of the match for Tennyson.
FC Rosette’s relegation was all-but confirmed by their 4-1 loss at home to Scalby in division two.
The visitors made a flying start with goals from Mikey Hartnett and Dan Peel putting them 2-0 up and then a 20-yard effort from Elliott Spurr struck the upright and the rebound was slotted in by Scalby man of the match Shaun Scales.
Rosette made a positive start to the second half and pulled a goal back with a looping shot from Sam Loy, but the three-goal lead was restored when Scales set up player-boss Dan Argyle and his effort was deflected in by a home defender.
Paul Robinson was named as the Rosette man of the match, the former Scarborough FC keeper making a series of fine saves for the Newby-based side.
Cayton Corinthians earned a 3-1 win at nine-man Athletico2B.
Luke Newbold’s 30-yard wind-assisted shot put Cayton in front and Mikey Dennis’ stunning volley after a great move made it 2-0 to the villagers.
Sam Swift’s header gave the Cats hope of a comeback but Josh Venner’s 10-yard finish after another good move sealed the points for Cayton.
Veteran Mark Gamble was the man of the match for Athletico2B, while Dennis excelled in central midfield for the victors.
Filey Town pulled six points clear at the top of the first division after romping to a 15-0 win at relegated Ayton.
James Pinder banged in six goals for Town while Phil Dickens also smacked in five, with other goals coming from Ben Briggs (2), Ricky Tomlinson and veteran Chris Duley.
Young defender James Reddish was named as man of the match for Ayton, who kept battling throughout despite the scoreline.