Smith returned an interception 100 yards for a touchdown while Hali turned a fumble into a score as Kansas City stayed perfect with a 23-13 win over the Bills.
The win is the Chiefs' first in Buffalo since 1986 and keeps them as the last remaining unbeaten team in the NFL at 9-0, matching the best start in franchise history.
Kansas City's offense gained just 210 yards to Buffalo's 470 as quarterback Alex Smith completed 19 of 29 passes for 124 yards.
Jeff Tuel was the most recent in a string of backups that have gone against the Chiefs' vaunted defense. He looked like a top-of-the-depth chart talent in the first quarter, finding Marquise Goodwin for a 59-yard score and a 7-0 lead.
Only Ryan Succop got Kansas City on the board before halftime with a 27-yard field goal. Buffalo kicker Dan Carpenter chipped in a 26-yard to give the Bills (3-6) a 10-3 lead before the teams headed to the locker rooms.
Smith's game-changing pick game at the 10:58 mark of the third quarter. It was the fourth chance Buffalo had to punch in a score from Kansas City's one-yard line. It was the second interception of the day as Kendrick Lewis hauled in the other before halftime.
Hali's scoop and score came when Marcus Cooper batted the ball out of T.J. Graham's hands after a reception with 12:47 left in the fourth quarter.
Succop added field goals from 41 and 39 yards out.
Jamaal Charles, who avoided the end zone for the second straight week, carried 17 times for 90 yards while hauling in six passes totaling six yards.