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SAN DIEGO -- This wasn't about changing defensive coordinators in midseason. It was about making a play that quite possibly saved the San Diego Chargers' season.

Burned by a pass interference call and then a touchdown catch by star tight end Tony Gonzalez, strong safety Clinton Hart swatted away Tyler Thigpen's 2-point conversion pass intended for Gonzalez with 23 seconds left to preserve the Chargers' 20-19 win over the lowly but scrappy Kansas City Chiefs on Sunday.

"As the call happened, I said to myself, I wasn't going to let him score this 2-point conversion," Hart said.

"We knew they were going for the win. Denver did it, and I guess they figured they could do it. But surprise, surprise, we stood up and made a difference," Hart said.

Coincidentally, San Diego lost to Denver 39-38 in Week 2 when the Broncos made a last-minute 2-point conversion.

San Diego's defense played so erratically in the season's first half that defensive coordinator Ted Cottrell was fired and replaced by inside linebackers coach Ron Rivera.

Despite coming off their bye, the Chargers (4-5) looked lethargic in the first half and were booed heading to the locker room trailing 13-6.

Philip Rivers rallied them with two touchdown passes late in the game, then Hart saved them.

Thigpen moved the Chiefs (1-8) to the Chargers 18 with 41 seconds left. On a second-down pass, Hart came from the side to knock a pass away from Gonzalez and was called for a questionable pass interference penalty that gave the Chiefs a first-and-goal at the 1. After an incomplete pass and a 2-yard loss by fullback Mike Cox, Gonzalez caught a 3-yard touchdown pass to pull the Chiefs within one. Hart and nickel back Antoine Cason were covering Gonzalez tightly.

Then came the big play. Hart deflected Thigpen's pass right to Quentin Jammer, who made the interception while on the ground.

"I got into him really good," Hart said. "I pressed him. He gets his big body and tries to push you off, and he tried to push me off. I latched onto the inside of his pads and I said 'I'm not going to let you push me off.' And I kind of got underneath him, got the ball down. Jammer got a pick."

Gonzalez thought there should have been a flag.

"It was ridiculous, he held me," the tight end said.

Hart disagreed.

"If he pushes me off, they're not going to call it," Hart said. "I said to myself, 'I'm not going to let him push me off because if I'm holding my ground, I've got a right to my spot.' That's what I did. I held my ground."

Gonzalez had 10 catches for 113 yards and two touchdowns.

"At that point, the way my game was going, I felt like that was all he could do because if he would given me an inch, I thought like Tyler was going to throw it up there, and obviously I'm taller than him and maybe I could have made that play," Gonzalez said. "But you never know. That's just confidence speaking. He's a good football player. It was a good battle. Give him credit."

Gonzalez knew the Chiefs were going for 2.

"It's a situation obviously for us, with only one win this season, let's go for it," he said.

"When you're 1-7, it isn't even a question of what you do. These guys deserve to win football games," coach Herm Edwards said.

Playing his fourth game, Thigpen was 27-of-41 for 266 yards and three touchdowns.

The Chargers' defense played much better after allowing two long scoring drives in the first half. Before the Chiefs' final TD drive, they had gained only 46 yards on 18 plays in the second half.

"We understand that, hey, if we don't get this going, it might be more than just D-coordinator changes," Hart said.

Asked if he saw improvement in the defense, Chargers coach Norv Turner said: "I think we made some stops that were big-time and that's an improvement."

Rivers threw a 5-yard touchdown pass to Malcom Floyd to tie the game late in the third quarter, then hit tight end Antonio Gates on a go-ahead, 8-yard score with just less than 7 minutes left.

Gates' TD gave the Chargers their first lead of the game. San Diego remained one game behind Denver in the anemic AFC West.

Rivers completed 27 of 36 passes for 316 yards.

Thigpen, who started the season as the Chiefs' third-string quarterback, outplayed Rivers in the first two quarters. He finished off long drives by throwing scoring passes of 30 yards to Mark Bradley and 34 yards to Gonzalez.

The Chiefs never got off the PAT after Gonzalez's first TD because of a low snap by Thomas Gafford, who was playing his second game in relief of the injured Jean-Philippe Darche. Holder Dustin Colquitt attempted a pass but it was tipped.

Game notes

LaDainian Tomlinson passed O.J. Simpson and Corey Dillon for 15th place on the career rushing list at 11,279 yards. He gained 78 yards on 22 carries against the Chiefs. ... Gonzalez tied Hall of Famer and former Charger Kellen Winslow with his 24th career 100-yard receiving game, tops among tight ends.