SAN FRANCISCO (AP) -- The St. Louis Rams arrived in San Francisco ready to grab some momentum for the December push with a third straight victory.
They even caught a break when 49ers left tackle Joe Staley went down with a knee injury early, providing a possible opening to get more pressure on quarterback Colin Kaepernick.
Yet Kaepernick shined with a healthy receiving corps at last as Michael Crabtree made his season debut, and San Francisco's stingy defense flustered Kellen Clemens all day in the Rams' 23-13 loss Sunday.
"We went into the ballgame knowing that it was going to be a slug-out kind of physical game up front," coach Jeff Fisher said. "We would have liked to carry on what we've been doing over the last couple of weeks, but for some reason we didn't match up well against these guys."
Crabtree's return opened up the field all the more for Anquan Boldin -- not to mention Vernon Davis and his high-hurdle show.
Boldin caught nine passes from Kaepernick, Crabtree made his long-awaited debut six months after Achilles tendon surgery, and the 49ers pressured the Rams defense from every angle.
On the other side of the ball, St. Louis managed only 73 total yards in the first half and regularly thwarted drives with its own mistakes.
Clemens went 19 of 37 for 218 yards with a late TD pass in a dismal afternoon by the Rams (5-7), who were trying for their first three-game winning streak of the season.
"There were some plays out there that we had opportunities to make which would have gotten us into a little bit of a better rhythm offensively," Clemens said. "We didn't make them."
The Rams committed 11 penalties for 105 yards. They settled for a 43-yard field goal by Greg Zuerlein just before halftime in their best drive to that point, then Zuerlein kicked a 34-yarder in the third quarter. St. Louis scored a late touchdown against the second-team defense.
Kaepernick went 19 of 28 for 275 yards and Frank Gore ran for a 3-yard touchdown as the reigning NFC champion Niners (8-4) boosted their position in the playoff picture. Crabtree had a 60-yard catch, while Vernon Davis hurdled into the end zone on a 17-yard touchdown reception.
With Hall of Famer Jerry Rice in the house, Boldin had six receptions in the first half on the way to his second-most productive game of the year behind his 13-catch performance in the season opener against Green Bay.
Crabtree, San Francisco's leading wide receiver during last season's Super Bowl run, had two catches just more than six months after he tore his right Achilles tendon and had surgery. Just having him on the field kept the St. Louis defense from focusing all its attention on Boldin and Davis.
"He's a big physical receiver, and his presence out there is definitely felt," linebacker James Laurinaitis said of Crabtree. "You have to pay attention to him. Whenever you have big receivers, physical guys like Boldin and Crabtree, and you have to worry about the speed of Vernon Davis ... they have a lot of weapons."
Davis displayed his athleticism with a new signature move, and did so not once but twice: a high hurdle over defenders. He led with his right foot while leaping over safety Rodney McLeod in the first half, then again to reach the end zone on his team-leading 10th touchdown catch. Davis also was tackled by T.J. McDonald with a prolonged, painful grab to his crotch. That was a first in his career.
"I was hurting," Davis said.
A year after the teams left Candlestick with a 24-24 tie, the 49ers methodically took care that it didn't happen again. They made it consecutive commanding victories in a short week following a 27-6 win at Washington on Monday night that snapped a two-game skid.
While Kaepernick was sacked four times, Robert Quinn and the opportunistic Rams defense failed to make the game-changing plays it had the past two weeks -- even when Staley was lost to a right knee injury early in the game. The St. Louis defensive line had scored touchdowns in each of the previous two games.
The 49ers held the Rams in check before the second-team defense surrendered Brian Quick's 3-yard touchdown catch with 18 seconds remaining.
St. Louis lost left tackle Jake Long late in the third quarter to a concussion after he collided into running back Zac Stacy, who played after dealing with concussion-like symptoms following a win against the Bears.
"He's going to have to undergo the concussion protocol," Fisher said. "He's already started it."
NOTES: Stacy had 72 yards on 19 carries. ... Rams C Scott Wells suffered an ankle injury.
AP NFL website: www.pro32.ap.org
Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.