Demarcus Robinson, a former Rams player, showcased his speed that the Rams had seemingly forgotten.
He turned the tables on his former team, hauling in a 39‑yard touchdown pass from Brock Purdy, giving San Francisco a 10‑7 lead with 4:28 remaining in the second quarter.
Cornerback Renardo Green set up the 49ers when Rams safety Quentin Lake intercepted Purdy earlier, and Green later logged an interception of Matthew Stafford on the seventh play of the drive.
San Francisco marched 86 yards in nine plays to score their first touchdown.
Purdy finished 15 of 22 for 134 yards, a touchdown and an interception. Mike Evans recorded five receptions for 47 yards.
Stafford completed four of ten passes for 65 yards, including an interception.
