SAN FRANCISCO — Alex Cobb had one of the toughest lineups in baseball before him. Armed with his devastating splitter, he quieted the defending champions in the Giants’ 3-2 win against the Braves on Monday night. Cobb held the Braves scoreless through seven innings, striking out seven batters and allowing six hits with no walks. He held them off balance with a splitter 61 times and got 12 swings-and-misses off of it. The Giants gave him some run support against one of baseball’s best young pitchers in Spencer Strider, scoring two by creating plenty of traffic on the base paths. Brandon Crawfor…