SAN DIEGO — Clinton Hart and the San Diego Chargers avoided the kind of upset that really could have ruined their season.

Hart, the strong safety, knocked down Tyler Thigpen's 2-point conversion pass with 23 seconds left and the Chargers held on to beat the scrappy Kansas City Chiefs 20-19 today.

The Chiefs pulled within one on Thigpen's 3-yard pass to tight end Tony Gonzalez. The Chiefs went for the win, but Thigpen's pass to Gonzalez was deflected by Hart to cornerback Quentin Jammer, who made the interception while on the ground.

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

The Chargers were booed off the field Sunday while trailing 13-6 at halftime, but rallied behind Philip Rivers in the second half.

Rivers threw a 5-yard touchdown pass to Malcom Floyd to tie the game late in the third quarter, then hit star tight end Antonio Gates on a go-ahead, 8-yard score with just less than 7 minutes left. Rivers completed 27 of 36 passes for 316 yards.

Gates' TD gave the Chargers (4-5) their first lead of the game. San Diego remained one game behind Denver in the anemic AFC West.

The outmanned Chiefs (1-8) were scrappy early, but missed a chance for just their second victory in more than a calendar year.

Rivers, who came in with a league-best 107.8 passer rating, led a 14-play drive that started on the last play of the third quarter and ate up the first 8:28 of the fourth period. He capped it by finding the wide-open Gates.

Rivers hit a similarly wide-open Floyd two possessions earlier.

But Rivers was intercepted twice, by safety Bernard Pollard in the end zone late in the second quarter, and by safety Jon McGraw late in the third quarter. The Chiefs didn't capitalize on either turnover.

Coming off their bye, the Chargers had lost three of four, including a two-loss, 11,000-mile road trip through Buffalo and London, where they fell to the Saints.

Thigpen, who started the season as the Chiefs' third-string quarterback, outplayed Rivers in the first two quarters. Thigpen threw scoring passes of 30 yards to Mark Bradley and 34 yards to Gonzalez to give the Chiefs the 13-6 lead at halftime.

The Chargers changed defensive coordinators during their bye week, firing Ted Cottrell and elevating Ron Rivera, but it didn't produce immediate results.

The Chargers allowed Thigpen to move the Chiefs 95 yards in 12 plays on their first drive, capping it with the pass to Bradley, who burned Jammer.

After the Chargers closed to 7-6 on field goals of 34 and 26 yards by Nate Kaeding, Thigpen moved the Chiefs 83 yards on seven plays, finding Gonzalez for his catch-and-run TD. The star tight end caught a short pass, made Hart miss, then got a nice block from Bradley as he made his way across the field before turning down the left sideline and into the end zone.

LaDainian Tomlinson passed O.J. Simpson and Corey Dillon for 15th place on the all-time rushing list at 11,279 yards. He gained 78 yards on 22 carries against the Chiefs.