BATON ROUGE, La. — In these kind of games, on these stages, the margin is agonizingly thin. One missed block, one errant throw, one incorrect path on a tackle attempt — games like these hinge on errors like those, so easily sandpapered over in other games. There was 10:10 left in the game Saturday at Tiger Stadium, and the place was awaiting a reason to come unglued, to send the cheers of 92,734 up into the night sky. South Carolina quarterback Connor Shaw was running left to escape a pass rush. He looked downfield, stopped and attempted an off-balance throw, trying to make something out of this third down and 6 at USC’s 29-yard line with the Gamecocks up by a point.

The throw sailed long, into free safety Eric Reid’s hands. He returned it 29 yards to USC’s 22. Death Valley, as they call this huge stadium, came to life. LSU converted the interception into just a field goal with 6:37 left, but a minute and 34 seconds later, on the first play of LSU’s next drive, Jeremy Hill ran 50 yards for a touchdown. The sea of yellow roared so loud they may have been heard in the Gulf of Mexico.

Third-ranked USC’s undefeated season died here Saturday, 23-21, in a gem of a game against ninth-ranked LSU (6-1, 2-1 Southeastern Conference).

It died not only because of Shaw’s interception, though that was a fatal blow. USC also got destroyed at the line of scrimmage. The Gamecocks ran for 34 yards, 1.4 per carry. The Tigers ran for 258, 4.9 per carry. LSU converted 11 of 19 third downs, USC three of 13. USC defensive coordinator Lorenzo Ward said USC had “by far” its worst tackling performance of the season.

Though perfection is gone, this season of hope remains intact for USC (6-1, 4-1). The Gamecocks, who hadn’t been ranked this high since they were No. 2 in 1984, will continue their three-game gauntlet next Saturday at undefeated Florida, a game that now looms larger.

Regardless of the USC-LSU result, the Gamecocks would still be in auspicious position to win the Southeastern Conference’s Eastern Division. But now, a loss to Florida could knock them out of contention. All of the Gamecocks must play better if they are to answer the LSU loss.

USC coach Steve Spurrier said he kept asking quarterbacks coach G.A. Mangus, about Shaw, “Did he get hit in the head somewhere?” The reason, Spurrier said later: “Because some of his decision making was a little off.”

Shaw offered no excuses for his pick, saying, “I was off balance. I should have flipped my hips and set my feet. I just kind of rushed the throw.”

Ward was equally as definitive regarding USC’s failure to stop the run: “We’ve got to stop the run if we’re going to win.”

Nor did Spurrier mince words, as he looked ahead to Florida, which leans on the run: “We better get a lot stronger on both sides of the ball.”

The Tigers, who trailed 7-3 at halftime, carved up USC on their first possession of the second half, cruising 69 yards in nine plays and 3:47 to score a seven-yard rushing touchdown and take a 10-7 lead with 11:13 left in the third quarter.

The Gamecocks answered with a two-yard touchdown run by Marcus Lattimore that put them up 14-10 with 5:11 left in the third quarter. USC got to the 2-yard line because of a pretty 30-yard pass by Shaw to leaping tight end Justice Cunningham, who had lined up wide. Shaw threw the ball back across the field and dropped it between two defenders — highlight of his night.

USC made admirable stands on back-to-back LSU drives. The Tigers had first and goal at the 9, and settled for a field goal. Then, on the possession after Shaw’s pick, they had first and goal at the 11 and did the same, to go up 16-14 with 6:37 left. In five red zone trips Saturday, LSU got one touchdown and four field goals, though the Tigers out-gained USC, 406-211.

The game was one of the most significant in USC’s history, just as last week’s win in Columbia over fifth-ranked Georgia. The Gamecocks were trying to start 7-0 for the second time ever, and the first since 1984, when they began 9-0. Riding a nation-best 10-game winning streak, they faced an intimidating setting Saturday. LSU has now won 22 straight home games — the country’s best current streak.