The San Francisco 49ers beat the Kansas City Chiefs 27-17 on Friday, but the Niners’ first-team defense is still a work in progress. We break down the film of the Chiefs’ first drive against the 49ers’ starting defense.

The San Francisco 49ers, under head coach Kyle Shanahan and defensive coordinator Robert Saleh, have a new defensive scheme in 2017. In their first preseason game, the 49ers defense showed flashes, as well as potential areas of improvement; the first drive of the game had a bit of both.

The 49ers started the 2017 NFL preseason with a touchback on their opening kickoff. The Kansas City Chiefs — winners of the 2016 AFC West — came out firing on first down.

The Chiefs line up in 21 personnel with their tight end in the slot. The 49ers are playing Cover 3 Press behind a 4-3 under front:

Chiefs head coach Andy Reid calls a deep pass play to wide receiver Tyreek Hill, who makes up for his short stature with his blazing speed.

Hill — the “Z Receiver” on this play — is off the line of scrimmage, across from the 49ers’ top cornerback Rashard Robinson:

Hill takes advantage of the extra distance between the two players with a quick move to the outside.

Even with his long arms, Robinson misses the receiver, and quickly attempts to recover:

Robinson can run, but very few can fly like Hill, who has a step on the cornerback:

The 49ers’ stunt is ineffective, as Chiefs quarterback Alex Smith sees his open receiver, and heaves the ball down the field:

The 49ers’ single-high safety defense leaves Robinson with little protection over the top, as Hill catches the ball near the sideline:

Robinson’s combination of speed and hustle eventually forces the receiver out of bounds, but the Chiefs have a long reception for a first down: