The San Francisco 49ers are two quarters away from ending their three-game losing streak.

But they still have work to do to improve to 6-3 with a victory over a tough Jacksonville Jaguars team.

San Francisco leads 13-3 at the end of a half that revealed plenty about the NFC West leaders.

Deebo Samuel's return makes immediate difference

The 49ers, after forcing a Jags three-and-out on the first series, went 57 yards in four plays to take a 7-0 lead on a 13-yard touchdown throw from Brock Purdy to Brandon Aiyuk.

That series started in a fashion that served an illustration of just how valuable the returning Deebo Samuel is to the San Francisco attack.

Indeed, San Francisco's first first down of the game came on a play that saw Samuel go in orbit motion before Purdy then executed a play-fake and found a wide-open Christian McCaffrey on the right sideline.

The most important aspect of the trade for McCaffrey last year was the stress he and Samuel put on defenses when they are both on the field, and it took only two offensive players for compelling evidence of their dual gravity.

Chase Young's instant impact

Right from the first snap, the 49ers' defense looked like a group reinvigorated, and that was before Chase Young even took the field.

When the 49ers' newest trade acquisition entered the fray, it did not take long for him to make an impression.

Young continued the same impressive form he displayed in the first half of the season for the Washington Commanders, helping Nick Bosa and Co. continually pressure a visibly uncomfortable Trevor Lawrence.

The highlight came on Jacksonville's fourth offensive series, as Young and Bosa delivered on the former's promise of the two ex-Ohio State teammates having a race to the quarterback, meeting at Lawrence and forcing a fumble to end a promising Jaguars drive.

Familiar failings keep Jaguars in the game

The main source of frustration for Kyle Shanahan will be some of the familiar failings from their three-game losing streak keeping Jacksonville in the mix to pull off a comeback. 

While the 49ers' run defense did an excellent job of stuffing runs up the middle, they remained vulnerable to rushes around the edge and continued to struggle defending the screens that helped Jacksonville get in position for their only points of the half.

On the other side of the ball, San Francisco did not take full advantage of their dominance, twice settling for field goals when deep inside Jacksonville territory.

Purdy took a third down sack on their second drive that got down to the 21-yard line, while an intentional grounding penalty after pressure on the quarterback from Travon Walker after the 49ers had driven down to the 11-yard line forced San Francisco to settle for another field goal.

Getting the ball to start the second half, the 49ers must make sure those missed chances do not come back to haunt them.

49ers vs. Jaguars inactives revealed

They have an answer on a key question.