I see this game a little differently.
The Giants just finished a 10 game homestand, which means they are playing their first game on the east coast against the Sox. Going west to east is always tougher than going east to west.
The Giants defense may be better--17 errors vs 24 errors--than the Sox, but their team ERA, 4.43, is ranked 25th in MLB to the Sox 1st. And they've scored 116 runs, ranked 21st in MLB, to the Sox 139, ranked 12th.
On the other hand, I completely agree with anyone who says a starting pitcher can make a huge difference, and Webb has thrown 8, 7, 7, and 7 innings in his last 4 starts, giving up a total of 3 runs. He is not a K guy, but is apparently terrific at getting outs. His ERA of 2.33 is his best ever, and tonight he is going on 7 days rest.