SANTA CLARA, Calif. — Running back Frank Gore ran for 107 yards, quarterback Colin Kaepernick passed for 201, and the San Francisco 49ers defeated Kansas City 22-17 on Sunday, ruining Chiefs quarterback Alex Smith’s homecoming.

Smith, facing the 49ers for the first time since they traded him to Kansas City following the 2012 season, completed 17 of 31 passes for 175 yards and two touchdowns and one interception, which ended the Chiefs’ final drive.

Kaepernick unseated Smith as the 49ers’ starting quarterback with seven games remaining in the 2012 season. He completed 14 of 26 passes with one touchdown and no interceptions.

Phil Dawson connected on all five of his field goal attempts for the 49ers, including two of over 50 yards, providing the game’s final nine points after Kansas City took a 17-13 lead in the third quarter.

Gore, who rushed for 119 yards last week against Philadelphia on 24 carries, needed just 18 carries to crack the 100-yard barrier.

The 49ers built a 13-10 halftime lead, but the Chiefs moved on Smith’s 17-yard touchdown pass to rookie wide receiver De’Anthony Thomas with 11:56 left in the third quarter.

Thomas, who missed the first four games of the season, scored on his first career NFL reception. He also gave the Chiefs great field position on their 58-yard scoring drive with a 28-yard gain on his first NFL punt return.

San Francisco drove deep into Chiefs territory but settled for Dawson’s 52-yard field goal with 6:16 left in the third quarter after Kaepernick was sacked twice and tackled for a loss on a quarterback sweep.

Kaepernick wasn’t sacked in the first half, but the Chiefs sacked him four times in the third quarter — twice by defensive end Allen Bailey and once each by nose tackle Dontari Poe and outside linebacker Justin Houston.

The 49ers faced fourth-and-1 at their 29 early in the fourth quarter and lined up to punt, but the snap went to upback Craig Dahl, who bulled three yards for a first down.

Then on 3rd-and-10 from the 49ers’ 32, wide receiver Brandon Lloyd made an acrobatic 29-yard catch, soaring above cornerback Sean Smith. Six plays later, Dawson kicked a 27-yard field goal, putting the 49ers back ahead 19-17 with 8:42 remaining.

After forcing the Chiefs to go three-and-out, the 49ers took over on their own 32 with 7:10 left to play. The 49ers stalled at the Chiefs’ 36 and lined up for a 54-yard field goal attempt, but Kansas City was flagged for having 12 players on the field, giving San Francisco a first down with 4:19 remaining.

The 49ers pounded their way to the 10 but settled for Dawson’s 30-yard field goal, giving them a 22-17 lead with 2:12 remaining.

The 49ers sealed the win when Smith overthrew tight end Anthony Fasano, and cornerback Perrish Cox intercepted at the Chiefs’ 43 and took a knee after a two-yard return to the 41 with 2:00 left.

Kaepernick completed 8 of 14 passes for 122 yards in the first half. Smith went 12 of 19 for 117 yards and a touchdown.

The Chiefs took the opening kickoff and marched 81 yards in 12 plays for a touchdown. Smith hit tight end Travis Kelce with a 2-yard touchdown pass with 8:37 left in the quarter.

Smith completed 6 of 8 passes for 61 yards on the drive, hitting Fasano three times for 32 yards and wide receiver Junior Hemingway twice for 27. Hemingway finished with a team-best four receptions for 50 yards.

The 49ers answered with Dawson’s 31-yard field goal, cutting Kansas City’s lead to 7-3 with 4:01 remaining in the opening quarter, but Kansas City’s Cairo Santos connected from 42 yards, making it 10-3 with 12:18 left in the half.

San Francisco scored the final 10 points of the half. Dawson drilled a 55-yard field goal, and Kaepernick threw a 9-yard touchdown pass to wide receiver Stevie Johnson, capping a 13-play, 93-yard drive that took 6:39.

NOTES: TE Vernon Davis (back), OT Anthony Davis (ankle, knee) and cornerback Tramaine Brock (toe) were among the 49ers’ inactives. … Chiefs WR Donnie Avery (sports hernia) and SS Eric Berry (ankle) were inactive. … Kansas City WR A.J. Jenkins made his first career NFL start and faced his former team for the first time. … 49ers backup OG Joe Looney left the game early in the third quarter with a hamstring injury.