After Fry put the Gamecocks ahead from 40 yards out, Missouri's Andrew Baggett missed a 24-yard attempt off the left goal post.
Missouri (7-1, 3-1) could have all but locked up the SEC East with a victory, instead South Carolina (6-2, 4-2 SEC) moves to within one game of the Tigers for the division lead, with home games against Mississippi State and Florida remaining.
A sprain left knee kept Shaw from starting, but he entered the game in the third quarter and helped the Gamecocks score the final 17 points of regulation. He also threw a 15-yard touchdown pass on fourth down in the Gamecocks' first overtime to match the Tigers' Marcus Murphy's 1-yard scamper.
Shaw engineered fourth-quarter scoring drives of 65, 69 and 63 yards, and the Gamecocks knotted the score at 17 on a two-yard reception by Nick Jones with 42 seconds remaining. Ellington scored his first touchdown on a 6-yard catch with 12:13 remaining, and Elliott Fry added a 20-yard field goal with 5:03 left.
Mike Davis caught three screen passes on South Carolina's final scoring drive in regulation, partly making up for two fumbles in the first half. The Gamecocks turned the ball over three consecutive times in the second quarter, helping Missouri take a 14-0 halftime lead.
Davis, who led the conference with 125.6 rushing yards per game entering the night, committed his first miscue at the Missouri 29-yard line with 12:30 remaining in the half, and his second halted a 71-yard drive at the Tigers' 2-yard line with 5:46 left. He finished the night with 51 rushing yards and 99 receiving yards while backup Shon Carson added 27 on the ground and 14 through the air.
Davis' second fumble set the stage for a 96-yard touchdown pass from Mauk to L'Damian Washington on Missouri's ensuing drive. Two yards deep in his own end zone, Mauk found Washington streaking toward the middle of the field for an easy first down, and then the receiver eluded two tackles at his 45-yard line before being untouched the rest of the way. The pass was Missouri's longest since a 98-yarder from Pete Woods to Joe Stewart at Nebraska in 1976.
Mauk struggled out of the gate, throwing a pass dropped by defender Sharrod Golightly and then an interception to Kaiwan Lewis, a far cry from the 41-yard pass and 20-yard touchdown toss he threw in his opening attempts last week in a 36-17 win against Florida. But Mauk then completed three of his next four to set up Missouri's first touchdown, an 11-yard scamper by Murphy with 1:23 left in the first quarter.
The Tigers added a 27-yard field goal by Baggett with 6:46 left in the third quarter before he missed a 46-yarder in the fourth quarter wide left.
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