BOSTON — David Pastrnak and Tommy Wingels scored 51 seconds apart in the second period, and Boston beat the Ottawa Senators 5-2 on Saturday night, preserving the Bruins’ chances for the No. 1 playoff seed in the Eastern Conference. Danton Heinen also scored for Boston, which added late goals by Noel Acciari and David Backes in the final two minutes to put away the Senators and complete the season sweep. Anton Khudobin stopped 26 shots for the Bruins, who host Florida on Sunday night in a game postponed by a winter storm Jan.