Kansas City quarterback Patrick Mahomes continued to dazzle as a first-year starter, passing for 314 yards and three touchdowns Sunday as the Chiefs toppled the San Francisco 49ers 38-27 in Kansas City, Mo.

The Chiefs (3-0) treated the crowd at their home opener in Arrowhead Stadium to five touchdowns on their first five possessions, all in the first half.

The loss could prove especially costly for San Francisco (1-2) after quarterback Jimmy Garoppolo was carted off the field in the fourth quarter with a left knee injury. Garoppolo finished 20 of 30 for 251 yards and two touchdowns.

The last of the Chiefs' touchdowns, a 12-yard pass to Sammy Watkins, was Mahomes' 13th touchdown pass of the season, enabling the former Texas Tech standout to break the NFL record of 12 touchdown passes in the first three games of a season set in 2013 by Denver's Peyton Manning.

Chris Conley and Demetrius Harris also snagged touchdown receptions for the Chiefs, who were limited to a field goal in the second half.

Kansas City scored on its first drive for the third time in as many games, converting a fourth-and-1 from the San Francisco 19 with a Mahomes keeper before the quarterback set up a 1-yard scoring burst by Kareem Hunt with a 16-yard completion to fullback Anthony Sherman. The Chiefs led 35-10 at halftime as Mahomes engineered touchdown drives of 57, 84, 75, 72 and 68 yards.

The 49ers trailed 14-0 when they responded early in the second quarter. Garoppolo found wide-open fullback Kyle Juszczyk for a 35-yard touchdown to cap a 75-yard drive.

However, the San Francisco offense had four drives of five or fewer plays in the first half.

The Niners finally got cranking in the third quarter against a Kansas City defense that came in ranked last in the NFL. Garoppolo engineered touchdown drives of 87 and 77 yards to pull San Francisco within 35-24 with 2:43 left in the third.

Garoppolo injured his left knee on a fourth-quarter drive as he was tackled near the boundary. Backup C.J. Beathard entered and threw an apparent touchdown pass on his first play, but it was nullified by offensive pass interference. The Niners settled for a 35-yard field goal.

As if the Chiefs needed any help, the 49ers committed 14 penalties resulting in 147 yards in mark-offs.

Niners cornerback Richard Sherman missed the second half with a calf injury.

--Field Level Media