Freshman quarterback Jake Bentley and an opportunistic South Carolina defense led the Gamecocks to a 24-21 upset of No. 18 Tennessee in the biggest win of coach Will Muschamp's first season on Saturday night at Williams-Brice Stadium in Columbia, S.C.

Bentley, making his first career Southeastern Conference start, threw two touchdowns, including a 35-yarder to K.C. Crosby that put the Gamecocks up by 10 early in the fourth quarter.

Tennessee again started slow and this time couldn't deliver any second-half dramatics in a crippling loss for the Vols' SEC East hopes. Kicker Aaron Medley was way short on a 58-yard field goal attempt as time expired.

The Volunteers (5-3, 2-2 SEC) now trail first-place Florida by two games in the SEC East.

"Unacceptable," Tennessee coach Butch Jones told reporters after the loss. "It starts with me, with the coaching staff."

South Carolina (4-4, 2-4) forced three turnovers in front of a raucous home crowd that saw the Gamecocks revive their hopes of reaching a bowl game in Muschamp's first season.

"We're a different team at home, in my short time here, as far as how our guys approach and play," Muschamp said in the postgame press conference.

"Our fan-base has a tremendous effect on us. I'm proud of our players. I told them to invest and asked them to continue to believe. If you just continue to do the things we ask you to do, we know we'll get there."

Trailing 24-21 with 3:50 to play, Tennessee quarterback Joshua Dobbs was picked off for the second time by South Carolina's Jamarcus King. Dobbs also lost a fumble in in an uneven performance for the senior, who has made a habit of leading second-half comebacks this season.

Bentley, on the other hand, shined, completing 15 of 20 passes for 167 yards with touchdowns to Crosby and Bryan Evans.

Dobbs completed 12 of 26 passes for 161 yards with a touchdown and the two interceptions.

South Carolina had a touchdown called back by a holding penalty and had to settle for a short Elliot Fry field goal that pushed the lead to 17-7 late in the third quarter. But Tennessee's Evan Berry completely flipped the momentum with an electric 100-yard kickoff return that got the Volunteers back in the game.

It was a jarring momentum-shift, and the Vols' defense followed by forcing a three-and-out. But the Tennessee offense, which was missing top playmaker Alvin Kamara, never really found a rhythm against what appears to be an improving South Carolina defense under Muschamp.

Bentley threw a 17-yard touchdown pass to Bryan Edwards, and Rico Dowdle had a touchdown run in the first half to give South Carolina a 14-7 lead at intermission. Jamarcus King's interception of Dobbs set up Bentley's touchdown pass to Edwards.

Dowdle, another one of South Carolina's promising freshman, had a big night, rushing for 127 yards on 27 carries. He was hurt on a tackle in the second half, but Muschamp said "he'd be fine"

"We put (the freshmen) on the field (and) we expect them to play at a high level," Muschamp said. "In order to win in our league, we have to. Only on Sunday, when we're having dinner, that's when we say, they're freshmen."

The Volunteers were inside South Carolina territory late in the second quarter, looking for a tying score. But on a fourth-and-2, after back-to-back Tennessee timeouts, Dobbs was sacked by Darius English to end the drive.

It was just one of several blunders by the Vols in a sluggish and sloppy first half. Tennessee was flagged for six penalties and managed just 98 total yards in the first half.

A disappointed Jones said the Volunteers were lethargic on the sideline and undisciplined, but still hopes for a strong finish to a season that began with a lot of hype. Tennessee was picked to win the SEC East in the preseason and seemed to be in control of the division after knocking off Florida in September. But they've now lost three straight games.

"We can't let this one loss define who we are," Jones said. "But obviously too sloppy.

"You mark my words as I sit here at South Carolina," Jones added. "There's a lot of football to be played."

NOTES: Tennessee RB Alvin Kamara missed the game with a knee injury that is expected to keep him out a few weeks. ... The four previous meetings between the SEC East rivals were decided by a combined 11 points. ... South Carolina defensive back Chris Lammons was ejected in the first half after being flagged for unsportsmanlike conduct. Replays showed Lammons threw multiple punches at a Tennessee player. ... South Carolina coach Will Muschamp went 4-0 against Tennessee while coaching Florida. ... South Carolina freshman quarterback Jake Bentley passed for 201 yards and two touchdowns in his collegiate debut last week in a 34-28 win over UMass. Bentley is the son of Gamecocks running backs coach Bobby Bentley.