For a while, it seemed like Kansas City's opening game against the San Diego Chargers would be a grave disappointment.

But the Chiefs rallied from 21 points down for the biggest second-half comeback in franchise history Sunday afternoon, as they defeated the Chargers in overtime, 33-27, and improved to 1-0 on the season.  

After running back Spencer Ware tied the game with a touchdown late in the fourth quarter to force overtime, the Chiefs won the overtime toss and received the ball.

Starting at the Kansas City 30-yard line, quarterback Alex Smith handed the ball off to Ware, who brought it to the 50 with a 20-yard run. Ware followed the play with a 13-yard run into Chargers territory. A couple plays later, Smith hit tight end Travis Kelce for a 15-yard gain, bringing the Chiefs to the San Diego 8-yard line.

Facing third-and-2 from the San Diego 2, Smith took it up the middle himself for the walk-off touchdown and victory.

Though the Chiefs were able to get the win, the first half was an entirely different story.

The key play of the first offensive drive for the Chargers came on third-and-6 at the San Diego 43-yard line. Rivers dropped back as the Chiefs defense brought a blitz. The Chiefs were able to get to Rivers, but before falling to the ground, he got off a pass to wide receiver Tyrell Williams short to his left. Williams ran the ball 33 yards and into Chiefs territory.

Three plays later and after a defensive pass interference penalty, Gordon took the ball in 1 yard for the touchdown and a 7-3 San Diego lead.

In the second quarter, the Chargers offense continued to roll. Rivers orchestrated a 13-play drive that finished with a 6-yard touchdown run from Gordon, and then the Chargers defense forced the Chiefs offense to a three-and-out possession. Smith was sacked for a loss of 9 yards by Caraun Reid on first down, then Jerry Attaochu for a loss of 14 on third down.

The Chiefs punted the ball back to the Chargers, who would score again on the next possession. Despite facing first-and-20 at the Kansas City 27-yard line, the Chargers had consecutive passes of 7, 8 and 8 yards for first-and-goal from the Kansas City 4.

Rivers hit Danny Woodhead in the end zone for a wide-open 4-yard touchdown reception and a 21-3 lead into the half.

The Chargers opened scoring in the second half with a 29-yard field goal to take a 24-3 lead, and the Chiefs began to mount their comeback on the ensuing possession.

On the very first play of the drive, Smith hit Ware on a pass down the middle of the field for a 45-yard gain. When the Chargers forced fourth-and-5 at their own 25-yard line, Chiefs head coach Andy Reid opted to go for it, and Smith converted the fourth-down attempt by finding Kelce for a 13-yard gain.

Two plays later, WR Tyreek Hill had a 9-yard reception for the first Chiefs touchdown of the season.

San Diego responded with a 28-yard field goal to make it 27-10 early in the fourth quarter.

On the next possession, Smith intended to find WR Jeremy Maclin, but Chargers cornerback Jason Verrett stepped in front of the pass and made a diving interception. Resulting from the turnover, the Chargers attempted a 55-yard field goal, but it was no good, giving the Chiefs good field position.

On the next drive, the Chiefs faced fourth-and-2 once again at the San Diego 48 yard-line, which they converted with a 7-yard pass to RB Charcandrick West. After a 12-yard gain from Ware, Smith went to Maclin on back-to-back plays, including a 19-yard throw-and-catch down the left sideline for a touchdown. The Chiefs trailed the Chargers, 27-17, with less than 10 minutes left in the game.

The Chargers offense blanked on the next drive, then the Chiefs got even closer with a 33-yard field goal to make it 27-20.

After another key stop by the Chiefs defense, Chargers punter Drew Kaser muffed the kick and the ball only went 17 yards before it sailed out of bounds.

Starting at the San Diego 42-yard line, Smith hit West to his right for 7 yards. On the next play, Smith threw the ball 22 yards down the middle of the field to Maclin, who was quickly hit by Jahleel Addae with helmet-to-helmet contact, which drew a personal foul. From the 5-yard line, Ware ran it in for the game-tying touchdown and overtime.

Ware had a career day for the Chiefs, recording 70 yards rushing on 11 carries and a touchdown, along with 129 yards receiving on 7 receptions. Smith finished 34 of 48 for 363 yards and 2 touchdowns. CB Steven Nelson and LB Justin March shared the team lead in tackles with 9 apiece. LB Dee Ford had 4 tackles and a sack.

WR Keenan Allen, who had 6 receptions for 63 yards, left the game on a cart with a knee injury late in the second quarter. Maclin briefly left the game during the fourth quarter to be evaluated for a concussion, but he later returned.

The Chiefs head down to Houston for their Week 2 matchup with the Texans next week. The game time is 12:00 p.m. CT.