ATLANTA — A.J. Ewing is not deterred by left-handed pitching. The rookie homered and singled — both against lefties — to finish 2-for-4 in the Mets’ 10-9 victory over the Braves on Sunday. It marked the second time Ewing had multiple hits against left-handers in a game this season. Ewing launched a Martín Pérez sinker for a homer leading off the third inning. The blast, which cleared the center field fence, was the first of his career that he did not pull. Ewing has five homers. “I think I have always been comfortable against lefties,” he said. Ewing and Carson Benge, the two rookies in the lineup, have been success stories in a dreary season for the Mets. The 21-year-old Ewing boosted his OPS to .756 with his latest performance. “I think we have believed he’s going to hit lefties in the l