BOSTON — Daniel Robertson has been more pained by his slow start than anyone.So hitting his first homer of the season, and coming against the Red Sox and Chris Sale (against whom he was 0-for-11), and giving the Rays a first-inning lead on their way to a series-sweeping 5-2 win Sunday made it even better.“It felt good,’’ said Robertson, hitting .176 overall. “To do it here, early in the game to get us going, off an elite pitcher I’ve faced quite a bit through my big-league career and haven’t had much success off, that definitely felt really good."Not just for personal reasons but just to contribute to the team and get us going early. That’s what felt good.’’ On Saturday the bullpen caused a lot of stress as the Rays had to use five relievers to get the final nine outs, with Emilio Pagan saving the day, and the game, his third straight such opportunity.Sunday was a little less dramatic.Pagan was used to get the final out of the seventh, then Jose Alvarado zipped through the top of the Sox order in an eight-pitch eighth. The Rays added a run, then Diego Castillo, who has been in a bit of a rut, allowed just a one-out single in a 12-pitch ninth to log the save and seal the win “That was big,’’ manager Kevin Cash said. “The fifth run helped a lot. But for Diego to come in and have a quiet inning was big for his psyche, it had to have been.’’ 28-4 First-inning scoring margin for the Rays, with the most runs scored and the fewest allowed in the first of any team, and the largest margin of any team in any inning.. “They’re good. They have a great pitching staff.’ ’Red Sox manager Alex Cora, on the Rays• At 18-9, the Rays are off to the third-best 27-game start in franchise history, behind 2010 and 2012.• Ryne Stanek is the opener for Monday’s series opener in Kansas City, with Yonny Chirinos expected to work the bulk of the innings.• The Rays are 8-1 in series play, 4-0 on the road.