Walker carded two consecutive 73s on the final day to finish six shots in arrears of McKenzie on 284 (70 68 73 73).
The Yorkshire golfer was two under after six holes of his third round, but came home in 38 for his first 73 of the day.
In the afternoon he went to the turn in two-under 34, but suffered three bogeys on his back nine.
Tied 13th was Bawtry’s Ben Brewster who recovered well from bogeys at the first two holes in the morning by birdieing both three and nine. Three birdies in a five-hole inward stretch were tempered by the infusion of a couple of bogeys, but he just dipped under par with a 71.
He was a further four shots over par by his 10th afternoon hole before playing the last seven in one under for a 75 and a 288 tally (68 74 71 75).
Ben Hutchinson, of Howley Hall, endured two debilitating triple bogeys at four and seven as well as a double at the 15th in his morning 80.
He saw three shots go in the space of two holes in his afternoon outward nine, but showed great spirit to card four birdies in his last 10 holes for a 73 and 293 aggregate (69 71 80 73) for a share of 28th.
McKenzie (67 69 70 72) finished two clear of runner-up Ben Westgate, of Trevose.