Brock Purdy suffered through one of the worst games of his young NFL career in Sunday’s 28-18 home loss to Kansas City.

Playing the second half without his top three wide receivers — Brandon Aiyuk (knee), Deebo Samuel (illness) and Jauan Jennings (hip) — the 49ers made things close with an impressive third-quarter drive.

Then, the bottom fell out.

Purdy tossed back-to-back interceptions, his second and third picks of the day. The third-quarter INT was a woeful miscommunication between the QB and receiver Ronnie Bell. Purdy and Kyle Shanahan confirmed after the game that the error was on the QB for sailing the throw.

“I think I’ve just got to play better for sure just with my throws and some decisions. That’s pretty simple,” Purdy said, via NBC Sports Bay Area. “I’ve obviously got to watch the film again and stuff, but my instant reaction is I’ve got to play better. The second interception was on me again. Ronnie did his job. I thought he just got hemmed up. I didn’t know where he was going to come out on his route, so I just tried putting it on him, and then he ended up breaking out pretty good. So, Ronnie did his job. It was on me.”

Purdy generated a career-low starting 36.7 passer rating in Week 7. His three interceptions were the second-most in a game in his career (four against Baltimore in Week 16, 2023). The Niners are 0-5 when Purdy has two-plus INTs.

Purdy was particularly poor on third downs, going 1-of-6 for 41 yards and two INTs (16.0 passer rating) versus Kansas City.

Missing so many weapons left the Niners ridiculously depleted. Beyond George Kittle, the Niners’ passing offense is a shell of itself. Fourth-round rookie Jacob Cowing led all wide receivers on Sunday with two catches for 50 yards. With Aiyuk’s prognosis not looking great, the Niners need Purdy to raise his game.

Purdy is 14-2 when Samuel, Christian McCaffrey and Trent Williams all play in his career. He is now 6-6 when one or more of them miss the game in his career.

“We didn’t do anything really good on offense,” Shanahan said. “I know he’d love to have all three of those picks back. Brock’s been playing unbelievable this year, done some good things on offense this year, but today wasn’t that day.”

Steve Spagnuolo’s defense has a way of discombobulating even the best QBs. A shorthanded one allowed the Chiefs to feast.