The San Francisco 49ers are on course for a third successive defeat.

San Francisco went into the half in the Week 8 clash with the Cincinnati Bengals trailing 14-10, as a Niners team many had penciled in for the Super Bowl after the first five weeks continued to show signs of vulnerability.

Despite the close half-time score, head coach Kyle Shanahan will likely have been far from happy with much of what he saw in the opening two quarters, with one specific side of the ball enduring significant struggles that will be a subject of severe scrutiny as the Niners head into the bye week.

Defensive issues abound for 49ers

The 49ers' defense was seeking a response after giving up 452 yards to the Minnesota Vikings.It did not produce it across the opening two series against the Bengals' offense.

Cincinnati had no problem moving the ball against Steve Wilks' group, averaging 6.9 yards per play. 

It was an all too familiar tale for the 49ers on that side of the ball, the Bengals finding joy with draw plays and screen passes while the Niners paid the price for failing to get home on pressures, most notably on 3rd and 10 on Cincinnati's opening drive when Joe Burrow escaped both Nick Bosa and Arik Armstead to move the chains with a completion.

Defensive strength has long since been a hallmark of the 49ers under Kyle Shanahan, but right now opposing attacks are finding it too easy on a unit that is devoid of answers, and it wasn't until Clelin Ferrell forced a potentially critical red-zone fumble from Irv Smith Jr. that the Niners showed any sign of resistance.

Purdy shows no signs of rust

San Francisco quarterback Brock Purdy was only cleared from the concussion protocol on Saturday having exhibited symptoms on the flight back from Monday's loss to the Minnesota Vikings.

Any thought that Purdy might look rusty after suffering a serious head injury was quickly extinguished, however, with the Niners signal-caller a clear bright spot from the first half.

Purdy ended the first half six of seven for 81 yards along with 43 rushing yards on four attempts. The offense, which averaged seven yards a play, is not the issue, though it could still be much improved.

Run game largely lifeless

While Purdy found success as a scrambler and Christian McCaffrey made NFL history by scoring for the 17th successive game, San Francisco's rushing attack was largely missing in action in the first half.

Prior to a 16-yard rush in the final seconds of the first half, McCaffrey had just 15 yards on five carries, while the 49ers had twice failed to convert on run plays on second and short.

The first of those failures came on the opening drive as the Niners went three-and-out, while the second saw Elijah Mitchell lose four yards with the 49ers made to settle for a field goal.

San Francisco left points on the board because of the run game's inability to convert in short yardage situations, and that could well come back to haunt them in another close encounter.

49ers inactives for Week 8 vs. Bengals

Two offensive stars are out.