SAN FRANCISCO — Tony Vitello wasn’t around for the final two innings Sunday. What he missed was one of the ugliest sequences so far during a rough start to the Giants season.The bullpen blew a lead in the eighth and kept digging the hole. When it was over, the Giants had a 5-2 loss to the New York Mets, had wasted a good one from Logan Webb, and had dropped three of four in the series. They’re 3-7 overall and have scored just 26 runs over 10 games. The Giants had nothing going against right-hander Kodai Senga until the sixth, when a Patrick Bailey bloop and stolen base ignited a two-run rally. Matt Chapman tied the game and Rafael Devers gave Webb a lead with a flare to center that was inches away from the outstretched glove of Luis Robert. Webb handed that lead over to the bullpen, which was a question mark coming into the season but a pleasant surprise for most of these first couple weeks. This was the first real test, though, and it couldn’t have gone much worse. Keaton Winn got the first crack at the eighth and gave up a couple of hits with one out. Erik Miller then entered and gave up three straight run-scoring hits, with another...