The Red Sox’ starting pitching has been their strength, their rock, their foundation this season. It’s been so good, the rotation went the first 16 games without allowing more than three runs in any start. That streak, as well as a seven-game winning streak, ended in Game 17 yesterday. In Game 18, the nightcap to a doubleheader, the Red Sox lost again, 5-4, in a game that featured a distressing effort from the bullpen but a very intriguing spot start from rookie Allen Webster in his major league debut. The loss in Game 2 came in the 10th inning, when reliever Andrew Miller loaded the bases on two hits and a walk, and then walked in the winning run. In the eighth inning, reliever Koji Uehara gave up a game-tying solo homer, ruining the chance for Webster to come out of his first big league appearance with a victory. Webster deserved a win after six innings and three runs (two earned) allowed on five hits and just one walk, with five strikeouts. Said Webster: “I felt great, I felt good. It was a neat experience, the fans were amazing.” His manager agreed. “I thought he showed great poise, good mound presence, showed very good stuff, similar to what we saw in spring training with the exception of a couple of fastballs that might have been a little bit elevated in the strike zone,” said John Farrell, referring to two home runs Webster gave up in the fifth inning. “He did everything we could have hoped in a spot start for us.