BOSTON — Andrew Benintendi has continued the hot hitting out of the leadoff spot for injured star Mookie Betts. Benintendi hit a three-run homer to cap a five-run fourth inning, J.D. Martinez added a solo homer, and the Boston Red Sox coasted to an 8-3 victory over the Toronto Blue Jays on Monday. With regular leadoff hitter Betts missing his second straight game because of tightness on his left side that he felt in batting practice Sunday, Benintendi added a triple and single, improving to 4 for 8 in the two days. “I’m seeing it pretty well right now,” Benintendi said in his usually quiet voice. Reminded that it was his first career homer over the Green Monster, the 23-year-old said: “I’ve hit a few over there in BP, but not in a game.” Betts entered the day with a major-league-leading .359 batting average. Jackie Bradley Jr.