The Gators (42-17) face Vanderbilt today for a shot at the championship. The Gamecocks (40-17) went 1-2 at Regions Park.
Johnson (7-4) pitched his first career complete game.
The Gamecocks had beaten Florida twice in the College World Series to claim the national title last season.
Florida led 7-0 before South Carolina got on the board in the sixth.
Tanner English beat out a grounder to shortstop to open the inning. He advanced to third on a single by Chase Vergason, the second hit of the night for the second baseman. English scored on a double play.
South Carolina added a run in the ninth when Evan Marzilli doubled to left field with two outs and scored on Christian Walker’s RBI single to left.
Nolan Fontana, Preston Tucker, Casey Turgeon and Josh Tobias had two hits each to lead Florida. Fontana scored three runs and Zunino drove in three.
Vergason finished 2 for 3 to lead South Carolina.
MISSISSIPPI STATE 4, LOUISIANA STATE 3 (10 INN.)
Matthew Britton's single up the middle brought home the winning run in Mississippi State's victory over top-seeded Louisiana State University.
Mitch Slauter drove a one-out double to the center field wall for the Bulldogs (37-22), who had rallied with two runs in the ninth and face Kentucky today for a berth in the championship game.
Jonathan Holder (2-0), who hasn’t allowed a run in 22 appearances this season, pitched around an error for a scoreless top of the 10th.
CLEMSON 9, FLORIDA STATE 7
In Greensboro, N.C., Jon McGibbon’s three-run home run in the ninth inning lifted Clemson past Florida State.
McGibbon finished with four RBI for the fifth-seeded Tigers (33-25). They can claim a spot in the championship game if they beat eighth-seeded Georgia Tech today in their Pool A finale.
Clemson trailed 7-6 entering the ninth when Phil Pohl singled with one out and was replaced by pinch-runner Dominic Attanasio.
Pinch-hitter Mike Dunster then singled, and McGibbon followed by sending Robert Benincasa’s 0-1 pitch over the fence in right-center.
Justin Gonzalez homered and drove in two runs for the top-seeded Seminoles (43-14). They fell to 0-2 in the round-robin tournament.
MIAMI 6, WAKE FOREST 3
Brad Fieger and Rony Rodriguez drove in two runs each to lead Miami (36-20).
Brett Armour knocked in two for Wake Forest (33-24).