49ers game grades: Potent game plan, Brock Purdy overcome new injuries, tiring defense

Head coach Kyle Shanahan's offensive game plan might have been the difference Sunday against the Cardinals as the 49ers overcame more injuries to improve to 3-0.   (Thearon W. Henderson/Getty Images) The San Francisco 49ers built a big lead and then traded late scores to get to 3-0 with a 36-30 win over Arizona, but as their banged-up defense got worked over by the Cardinals, the notch in the standings comes with increasing concern over what sort of roster the Niners will be fielding in the weeks ahead. Mike Evans became the third wide receiver carted off in three games, left tackle Trent Williams was forced out of action as well and the injury-depleted defensive line got worn down over the course of Sunday's victory at Levi's Stadium.

>Offense: A

>The 49ers struck quickly in their possessions, with Brock Purdy throwing four touchdown passes, the first coming on Deebo Samuel's 80-yard sprint on a hook-and-ladder play after a short completion to Evans. Evans would score his own TD subsequently before exiting with a rib injury, while tight end George Kittle's two fourth-quarter TDs re-emphasized the importance of his return to health with Purdy's receiving options starting to narrow. Christian McCaffrey keyed the ground game with a season-high 19 total touches and a TD, while the offensive line kept Purdy sack-free on the season.

>Defense: C+

>Being forced onto the field for 38:44 in a game is rarely a good sign, but the defense was struggling to end the Cardinals' possessions in the second half, a symptom of failing to create pressure while also not containing rookie running back Jeremiyah Love, who generated 109 total yards and a TD on 26 touches - none of them going for more than 8 yards. Two sacks and five QB hits might sounds like a lot, but the Cardinals got off 81 plays from scrimmage, and the defensive line generated just one of the sacks and two QB hits. Fred Warner (17 total tackles) and Renardo Green (13) led the swarm, but giving up 365 total yards to an offense steered by a journeyman like Jacoby Brissett is rarely a formula for victory.

>Special teams: C+

>Some sloppiness resurrects shades of past special teams snafus. Siran Neal getting hit by a Cardinals punt that Arizona recovered at the Niners' 28-yard line at the end of the third quarter, leading to a TD that brought the game within a single score early in the fourth, was the stuff of special teams nightmares, but could be written off as an unlucky bounce. Eddy Piñeiro missing two extra points could have been the difference had the Cardinals gotten another scoring opportunity. Samuel bobbled a kickoff return to boot. At least Piñeiro's lone field goal came from 57 yards out.

>Coaching: A

>Kyle Shanahan's game plan gets much of the credit here, as that hook-and-ladder play for the first score was inspired, but when the Cardinals narrowed the gap in the second half, trailing 23-20, the Niners' eight-play drive in response, culminating in Kittle's first TD reception, started with a completion to Kittle but brilliantly mixed things up with runs by McCaffrey, Samuel and Kaelon Black and targets for Kyle Juszczyk and KhaDarel Hodge (the latter erased by penalty). Even as the menu of options for Purdy might seem limited by injuries, Shanahan and his QB kept things cooking, as the 49ers generated 437 total yards on just 50 offensive plays, or 8.7 yards per play.

>Overall: B

>Yes, maybe it was "just" the Cardinals, but going 3-0 to start the season while the Seahawks suffered a surprising defeat in Washington is certainly a good place to be. However, the injury stacks at both wide receiver and on the defensive line threaten the 49ers' ability to sustain this success. Going up against the Broncos and then traveling to Seattle already represented an early, tough test for this team, but between the defense's apparent exhaustion, the mounting toll of injuries, and some emerging special teams concerns, there's going to be a lot of pressure on Shanahan, Purdy & Co. to keep conjuring up quick scores.

SubscribeThere’s more to San Francisco with the Chronicle. Subscribe today for just 25¢.This article originally published at 49ers game grades: Potent game plan, Brock Purdy overcome new injuries, tiring defense.