The San Francisco 49ers used a strong defensive effort in the second half of their Monday Night Football (MNF) game against the St. Louis Rams to turn a 14-10 halftime deficit to a 31-17 win in the National Football League (NFL).

The Rams raced to a 14-0 lead after the first quarter but the 49ers responded with a touchdown and a field before the end of the first half.

The first half was apparently St. Louis' last hurrah as San Francisco completely dismantled them in the second half getting outscored, 21-3 after the break. San FranciscoQB Colin Kaepernick finished with 343 passing yards on 22-of-36 completions with 3 TDs.

Brandon Lloyd (80 yards on 1 catch), Anquan Boldin (94 yards on 7 catches), Steve Johnson (53 yards on 5 catches) and Michael Crabtree (49 yards on 3 catches) all played well for San Francisco.

The 49ers improved to 4-2 for the season while the Rams dropped their fourth game in five outings so far in the regular season.

View the slideshow for more images from the 49ers vs. Rams game on NFL MNF.

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St. Louis Rams running back Benny Cunningham
St. Louis Rams quarterback Austin Davis (9) hands the ball off to St. Louis Rams running back Benny Cunningham (36) during the first half at the Edward Jones Dome. Reuters
St. Louis Rams running back Benny Cunningham
St. Louis Rams running back Benny Cunningham (36) dives into the end zone for a touch down against the San Francisco 49ers during the first half at the Edward Jones Dome. Reuters
St. Louis Rams cornerback E.J. Gaines
St. Louis Rams cornerback E.J. Gaines (33) tackles San Francisco 49ers wide receiver Steve Johnson (13) during the first half at the Edward Jones Dome. Reuters
St. Louis Rams running back Benny Cunningham
St. Louis Rams running back Benny Cunningham (36) leaps into the arms of center Scott Wells (63) after a one yard touchdown run during the first half against the San Francisco 49ers at the Edward Jones Dome. Reuters
St. Louis Rams tight end Lance Kendricks
St. Louis Rams tight end Lance Kendricks (88) catches a 22 yard touchdown pass during the first half against the San Francisco 49ers at the Edward Jones Dome. Reuters
St. Louis Rams tight end Lance Kendricks
St. Louis Rams tight end Lance Kendricks (88) celebrates after catching a 22 yard touchdown pass during the first half against the San Francisco 49ers at the Edward Jones Dome. Reuters
St. Louis Rams tight end Jared Cook
St. Louis Rams tight end Jared Cook (89) carries the ball for a 39 yard gain during the first half against the San Francisco 49ers at the Edward Jones Dome. Reuters
San Francisco 49ers tight end Vance McDonald
San Francisco 49ers tight end Vance McDonald (89) fumbles the football during the first half against the St. Louis Rams at the Edward Jones Dome. Reuters
St. Louis Rams quarterback Austin Davis
St. Louis Rams quarterback Austin Davis (9) celebrates after a touchdown during the first half against the San Francisco 49ers at the Edward Jones Dome. Reuters
San Francisco 49ers wide receiver Brandon Lloyd
San Francisco 49ers wide receiver Brandon Lloyd (84) beats St. Louis Rams cornerback Janoris Jenkins (21) and catches a 80 yard touchdown pass at the Edward Jones Dome. Reuters
San Francisco 49ers outside linebacker Dan Skuta
San Francisco 49ers outside linebacker Dan Skuta (51) attempts to tackle St. Louis Rams quarterback Austin Davis (9) during the first half at the Edward Jones Dome. Reuters
St. Louis Rams wide receiver Stedman Bailey
St. Louis Rams wide receiver Stedman Bailey (12) and St. Louis Rams cornerback Lamarcus Joyner (20) tackle San Francisco 49ers wide receiver Bruce Ellington (10) on a punt return during the first half at the Edward Jones Dome. Reuters
San Francisco 49ers wide receiver Anquan Boldin
San Francisco 49ers wide receiver Anquan Boldin (81) catches a 11 yard touchdown pass as St. Louis Rams cornerback Janoris Jenkins (21) defends during the second half at the Edward Jones Dome. Reuters
San Francisco 49ers quarterback Colin Kaepernick
San Francisco 49ers quarterback Colin Kaepernick (7) throws a touchdown pass to San Francisco 49ers wide receiver Brandon Lloyd (not pictured) against the St. Louis Rams during the first half at the Edward Jones Dome. Reuters
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