Alex Smith finished 21-of-36 for 223 yards and a pair of touchdowns, while Ryan Succop hit the deciding field goal early in the fourth quarter as Kansas City nipped Dallas, 17-16, in a Week 2 matchup from Arrowhead Stadium.
"When you're trying to build something, you need to win games like this," said Smith. "These are the games you look at in November and December. You need these types of wins, not only the caliber of the win but the style of win."
Dwayne Bowe and Jamaal Charles combined for 104 yards and two scores on 12 receptions for the Chiefs (2-0), who were coming off an easy win at Jacksonville to begin their 2013 slate.
Kansas City, under new head coach Andy Reid, has already equaled its win total from last season, which was a dismal 2-14 campaign under Romeo Crennel. Reid has a chance to guide the franchise to its first 3-0 start since 2010 this Thursday in Philadelphia, the city where he coached for 14 seasons through the end of last year.
Tony Romo was 30-of-42 for 298 yards and one touchdown for the Cowboys (1-1), who couldn't sustain momentum from last week's home win over the Giants.
Dez Bryant led all receivers with 141 yards and a TD on nine catches in defeat.
"We had a good plan and did some things that gave us a chance to win this football game. We put ourselves in position, but we didn't win it," Romo said. "Ultimately, that's all that matters."
Dallas marched 68 yards on its opening series of the second half, moving ahead 13-7 on a 30-yard make from Dan Bailey.
Kansas City countered on its next touch, as Smith found Bowe in the end zone for a 12-yard touchdown and 14-13 edge. Donnie Avery had the key reception in the series, a 31-yard gain to the Cowboys' 37 on 3rd-and-9.
On the next series, Lance Dunbar fumbled and Eric Berry recovered at the KC 47, returning the ball to the Cowboys' 31-yard line. The Chiefs' only gain on that possession was a 10-yard catch by Junior Hemingway on 3rd-and 11, but Succop drilled a 40-yarder one play later for a 17-13 advantage with 14:06 left in the fourth.
Romo was picked off by Berry with 4:06 on the clock, but Berry's holding penalty gave Dallas new life at Kansas City's 35-yard line. The visitors didn't gain a yard thereafter, and Bailey then booted a career-long 53-yarder to make it 17-16 with 3:50 remaining.
The Chiefs, who took over on their own 16 following the kickoff, held onto the ball until less than a minute remained. Charles picked up one first down on a 9-yard rush, a defensive pass interference call provided another set of downs, and then a Dustin Colquitt punt pinned the Cowboys in the shadow of their own goal line with 16 seconds to go.
Romo's pass to DeMarco Murray went for 14 yards on first down, but time ran out.
"Takeaways and points on both sides of the ball. We try to eliminate the turnovers and we try to score points," Reid admitted. "It's as simple as that."
The Chiefs made good on the first drive of the contest, going up 7-0 as Smith connected with Charles from two yards out to cap a 77-yard drive.
Bryant's 53-yard catch-and-run down the right sideline plus a pass interference call helped set up a 51-yard field goal from Bailey on Dallas' next touch.
Romo and Bryant starred on the following Cowboys' drive, connecting for 38 yards to the KC 6-yard line, a 5-yard strike on the next play and then the go- ahead TD from two yards out on 3rd-and-goal for a 10-7 game,
The teams traded punts throughout the second quarter, before Succop had a 57- yard attempt blocked in the final seconds of the half and the Chiefs trailed by three at intermission.
The Cowboys owned a 20-19 edge in first downs and outgained the Chiefs by a slim 318-313 margin ... Smith added 57 yards rushing on eight attempts ... Reid improved to 18-12 all-time against Dallas, with his last victory against the Cowboys coming as the Eagles' head coach in a 20-7 decision on Dec. 24, 2011 ... Despite the loss, Dallas has won six of 10 matchups against the Chiefs since the 1970 merger ... Murray was held to 25 yards on 12 carries ... Neither team fared well on third downs, with Kansas City going 4-for-13 and Dallas connecting on 3-of-11.