The streaking Mets rallied once again Saturday, pulling past the Braves in a two-run ninth inning that gave New York its sixth straight win, 6-4, and pushed the Mets’ lead in the National League East to 9 1/2 games over the fading Nationals. Second baseman Kelly Johnson knocked in the go-ahead run with a single to right, and hot-hitting center fielder Yoenis Cespedes — who blasted another home run in the eighth — added on a ninth-inning insurance run with a fielder’s choice grounder.