Here are position-by-position grades from the performance:
Before the comments go crazy, although it probably won’t make a difference, I try to keep these grades on leaguewide standards. Brock Purdy had an A+ performance given expectations for a rookie seventh-round pick forced into action, but compared to quarterback play around the league, he was unexceptional.
Before Purdy got hurt, Garoppolo had a pair of impressive downfield completions. Purdy averaged just 5.7 yards per attempt, ran into a couple of sacks, but he was a competent NFL quarterback. It was just one game, but Purdy already looks better to me than C.J. Beathard and Nick Mullins. While defenses will have time to prepare for him now, the Niners will bet on Kyle Shanahan scheming him past those challenges.
Running backs: A-
The 49ers backs averaged 4.2 yards per carry, but Christian McCaffrey did the bulk of his damage as a receiver. McCaffrey led the Niners with 8 receptions for 80 receiving yards and a touchdown, although he did have a drop. Jordan Mason was consistently a more productive runner than McCaffrey, and it could make it easier for Shanahan to limit the hits CMC takes by relying on Mason more in the rushing attack. Nevertheless, Mason was impressive on his 8 carries, amassing 51 yards.
Wide receivers: B-
Deebo Samuel, Brandon Aiyuk, and Jauan Jennings all had solid but unexceptional games, although Samuel had a couple of incredible plays to avoid big losses. The 49ers receivers other than Aiyuk have been struggling to get separation all season, and that could become an even bigger problem down the stretch if Purdy struggles to throw downfield more than Garoppolo. But that’s a problem for tomorrow.
Tight ends: D
Tyler Kroft had a 14-yard reception and probably would have had a touchdown if Purdy did not check down to George Kittle on a fourth-and-short. Kittle only had 2 receptions for 22 yards and committed a costly holding penalty.
Offensive line: B-
The 49ers quarterbacks were sacked four times, but all of them were not on the offensive line. Overall, Purdy generally had space in the pocket to extend plays. On the ground, the line was erratic, oscillating between generating big holes and absolutely no push. The 49ers will hope to get more consistency, but it was still a net positive.
Defensive line: A+
Nick Bosa. Enough said.
Tua Tagovailoa missed a lot of open receivers on Sunday (more on that later), but having to get his passes over Fred Warner played a big role. Warner only recorded two tackles because Miami barely ran the ball, but he had two passes defended and a garbage-time interception.
I have to admit that I thought Azeez Al-Shaair should have jumped Dre Greenlaw in the depth chart at various points over the past two seasons, but Greenlaw has proven the coaching staff right. Greenlaw led the team in tackles with 8 and added a pass defended and returned a fumble recovery for a touchdown.
Deommodore Lenoir and Jimmie Ward (who is more a nickel corner than safety at this point) each picked off Tagovailoa, and that lifts the corners up with the front seven. They had a tall task against the fastest receiving corps in the league and the Dolphins biggest plays weren’t because of their mistakes.
Massive mistakes by Tashaun Gipson and Talanoa Hufanga were responsible for the Dolphins' two touchdowns. Gipson took a terrible angle that enabled Trent Sherfield’s 75-yard touchdown on the first play from scrimmage and Hufanga whiffed on giving Mooney Ward help over the top on Tyreek Hill’s touchdown later in the game.
Special teams: A+
Robbie Gould made all his kicks. The 49ers prevented Miami from any big returns. Mitch Wishnowsky didn’t have any bad punts. Ray-Ray McCloud had a 31-yard kick return and averaged 17 yards per punt return.