A’s deal more damage to Mariners’ playoff hopes with walk-off in 10th

WEST SACRAMENTO – A season that seemed like it couldn’t get any worse for the Mariners did Friday night. A comeback that gave them the lead in the top of the 10th inning, and perhaps kept hope alive for a postseason bid, turned into a greater letdown, a 6-5 loss to the Athletics at Sutter Health Park when Donovan Walton hit a two-run home run in the bottom of the inning. George Kirby threw at least 100 pitches for the second outing in a row but found no joy in the accomplishment that surely saved bullpen arms — and in…