Mets ace Kodai Senga exited Thursday’s brilliant start against the Nationals with an apparent hamstring injury. After a 4-3 Mets win, he’s heading to the injured list, with an MRI scheduled Friday. This is a major blow to the MLB-best 45-24 Mets rotation, especially given Senga’s Cy Young-level performance and past injury struggles. His absence will test the team’s depth.