WASHINGTON — A couple of defensive slip-ups and a questionable relief option sealed the Amazin’s first loss of the year, a 4-2 defeat to the Nationals on Sunday at Nationals Park. The Nationals erased the Mets’ 2-1 lead in the eighth inning after right-hander Trevor Williams came in to relieve southpaw Chasen Shreve with no outs and a runner on first in a one-run game. The goal, which was not accomplished, for Williams was to retire the bottom of the Nationals lineup before it reached Juan Soto. Instead, Williams allowed a single to his first batter, Maikel Franco, to put runners on the corner…