SANTA CLARA, Calif. — San Francisco safety Eric Reid doesn’t pay attention to statistics, so it was news to him that the 49ers are ranked fourth in the NFC in passing defense and second in total defense.

“I’m more concerned about bringing a good defensive game,” Reid said of Monday night’s game against the St. Louis Rams. “It’s always on a week-to-week basis. We didn’t defend the run very well the first week against Dallas, so we came back and worked to improve that.”

The 49ers allow an average of 209 passing yards. One of the teams ahead of them in pass defense is the Rams, who allow 192.3 yards a game through the air.

Rams quarterback Austin Davis, who opened the season third on the depth chart, has the NFC’s fourth-best rating and is coming off his second straight 300-yard passing game.

“He looks like a standard NFL quarterback,” Reid, a former LSU standout, said. “He manages the offense. He’s there for a reason despite where he started the season.”

San Francisco coach Jim Harbaugh acknowledged that he was unaware of Davis at Southern Mississippi. The undrafted quarterback is in his third professional season, though he’s playing for the first time.

“I wish I would’ve been more aware of him. He looks like a real nice prospect,” Harbaugh said. “I am now.”

Harbaugh said he got excited about the Rams’ game with the Philadelphia Eagles as he watched the coaching tape, even though he knew the outcome.

“It was one of the rare times,” he said. “To watch them come back, sparks were flying. This was a quarterback that was making throws, an offense that was making plays. And then the last drive, they had a chance to win the game and I’m like, ‘Maybe they got the score wrong. Maybe the Rams really won this game,’ because he made a couple of throws in that drive there that were right on the money and gave his team the chance to win.”

Davis, who became the first St. Louis quarterback with back-to-back 300-yard and three-touchdown games since Kurt Warner in 2001, has been fearless in his willingness to challenge the secondary.

Reid said those deep threats were a source of concern for the 49ers and held their attention during preparation.

Rookie outside linebacker Aaron Lynch, who converted from defensive end, has seen his playing time increase weekly. He’s seen action in every game and has a pair of tackles. He’s still looking for his first career sack.

“It’s going to be exciting,” he said. “I mean, a sack is a sack and a tackle is a tackle. I don’t really differentiate between them. One is just behind the line.”