The 49ers got away with being road chalk of more than a field goal last Sunday because they were playing the Jets. The Giants aren't very good either, but they are not the Jets. They are a level higher. 
I don't see San Francisco escaping MetLife Stadium, a place it hates to play, with back-to-back road victories. The 49ers are just too banged-up. Yes, the Giants are down Saquan Barkley and Sterling Shepard. Barkley is their best player. Still, the Giants' injuries don't compare to how many key players are out for the 49ers. 
Let's start with defense where both the 49ers' line and secondary are heavily reduced with Nick Bosa, Solomon Thomas, Dee Ford and Richard Sherman all out. Bosa and Ford are the team's best pass rushers. Sherman is their best cornerback and a team leader. 
That's just on defense. Now go to offense where the 49ers are without their starting center, two best running backs, top wide receiver and oh yes, quarterback Jimmy Garoppolo. Kyle Shanahan can game plan all he wants, but he doesn't have the pieces to formulate anything other than a conservative just-try-to-get-alive-out-of-here mentality. 
It's not just physical with the 49ers. They are mentally not right about playing at this stadium believing the carpet helped cause some of their many injuries. 
The Giants are good enough to take advantage. They nearly upset the Bears on the road last week after losing Barkley early in the game. Daniel Jones has upside and other decent wide receivers besides Shepard. The Giants' defense also has made strides. 
At 0-2, the Giants are in must-win mode. The 49ers are going to take New York's best punch. I don't see them being able to withstand it in their crippled situation.