I gave him a C. He didn't make bad mistakes, but he didn't make too many big plays either. He missed on several throws that could have gone for big yardage or TD's. He had to be perfect on those balls, but this is the NFL.
You're right, down the stretch the 49ers tightened up their coverage and Tannehill just wasn't able to come up with any big throws late in the 4th. Our receivers weren't open by much (if at all), but they were open if Tannehill was able to make a perfect throw and throw his receiver open. But Tannehill's a rookie and he missed. Aside from the last five throws (unfortunately the biggest five throws of the game) he looked pretty good. He was smart with the football, he didn't turn it over, and he made some big plays down the field (unfortunately our receivers couldn't translate those throws into touchdowns).