Carolina appeared to have the game in hand after a 29-yard touchdown pass from Cam Newton to Brandon LaFell put the Panthers (2-8) up 21-10 with six minutes left in the game. But after a 40-yard field goal by Connor Barth, the Panthers' offense couldn't put the game away and had to punt.
Freeman led the Bucs 80 yards on seven plays in 50 seconds, despite not having any timeouts.
He finished the drive with a perfectly thrown 24-yard touchdown pass to Vincent Jackson between three defenders with 12 seconds left. Freeman went back to Jackson for a 2-point conversion on a slant route to tie the game and send it into overtime.
In overtime, the Bucs moved quickly down the field and Freeman found an open Clark along the left sideline for the game-winner.
Newton finished with 252 yards passing and a touchdown and Jonathan Stewart ran for 43 yards and a score for the Panthers, who failed to avenge a 16-10 loss to the Bucs in the season opener.
Of Carolina's last six losses, they've led in the fourth quarter in five of them.
The Bucs came in as one of the hottest teams in the league having scored an average of 35.6 points per game during the past five games.
But after scoring a quick 10 points, the Panthers defense shut them down for most of the remainder of the three quarters forcing three turnovers, including a 74-yard interception return for a touchdown by Captain Munnerlyn and a key fumble by rookie Doug Martin on a fourth-and-goal at the 1-yard line.
Trailing 14-10, the Bucs appeared ready to take the lead after driving 15 plays to the Carolina 1.
But on fourth down, Bucs coach Greg Schiano went for the touchdown instead of the field goal and linebacker Thomas Davis plowed into Martin, forcing the ball out near the goal line. Fellow linebacker Luke Kuechly, the team's first-round draft pick, recovered in the end zone for a touchback.
Officials reviewed the play to see if Martin got in, but the call stood.
The Panthers immediately cashed in on the change of momentum as Newton led the Panthers 80 yards on seven plays, converting two key third downs along the way. He capped the drive with a 29-yard scoring strike to a wide-open LaFell on a crossing route to make it a two-possession game at 21-10.
The Bucs would cut the lead to 21-13 Barth's field goal with 4:03 left in the game.
Tampa Bay would get one last shot and Freeman made the most of it. The Bucs got a big 15-yard penalty when officials ruled Davis hit a defenseless receiver in the head. But the big play was Carolina's inability to defend Jackson on the TD pass down the middle.
Things didn't start well for the Panthers on Sunday.
Less than a week after firing special teams coordinator Brian Murphy, Munnerlyn, who doubles as the team's punt returner, was hit by Jacob Cutrera and fumbled at the Panthers 29. Dekoda Watson recovered for the Bucs and six plays later, Freeman, found tight end Nate Byham in the back of the end zone for a touchdown and early 7-0 lead early midway through the first quarter.
The Bucs added to that lead later in the first quarter on Barth's 51-yard field goal.
And when Carolina's two leading sack artists, Charles Johnson and Greg Hardy, collided in the backfield and remained on the ground for more than minute while being attended to by trainers, it seemed this game might be ready to spiral out of control.
The game changed suddenly and unexpectedly a few plays later.
With two rookie defensive ends in the game, the Panthers got pressure on Freeman up the middle and he threw a weak ball toward the flat. That's where Munnerlyn made up for his earlier mistake by returning the ball 74 yards for a touchdown.
The Panthers came up with a defensive stop on their next possession and Newton drove Carolina 77 yards on eight plays with Jonathan Stewart scoring on a 1-yard touchdown plunge to give the Panthers a 14-10 lead.
Buccaneers 27, Panthers 21 (OT)
Tampa Bay 10 0 0 11 6 27
Carolina 7 7 0 7 0 21
TB • Byham 3 pass from Freeman (Barth kick), 8:46.
TB • FG Barth 51, 5:21.
Car • Munnerlyn 74 interception return (Medlock kick), :35.
Car • Stewart 1 run (Medlock kick), 8:53.
Car • LaFell 29 pass from Newton (Medlock kick), 6:00.
TB • FG Barth 40, 4:03.
TB • Jackson 24 pass from Freeman (Jackson pass from Freeman), :12.
TB • Clark 15 pass from Freeman, 10:40.
Attendance • 72,603.
First downs 25 18
Total Net Yards 403 331
Rushes-yards 30-167 34-97
Passing 236 234
Punt Returns 2-15 3-41
Kickoff Returns 1-33 3-59
Interceptions Ret. 0-0 2-92
Comp-Att-Int 25-46-2 16-29-0
Sacked-Yards Lost 1-12 2-18
Punts 6-49.5 6-45.7
Fumbles-Lost 1-1 1-1
Penalties-yards 6-50 11-91
Time of Possession 32:30 31:50
Rushing • Tampa Bay, Martin 24-138, Freeman 5-27, Ware 1-2. Carolina, Stewart 15-43, Newton 11-40, D.Williams 7-18, Nakamura 1-(minus 4).
Passing • Tampa Bay, Freeman 25-46-2-248. Carolina, Newton 16-29-0-252.
Receiving • Tampa Bay, Clark 7-58, Jackson 6-94, Martin 4-23, Williams 3-29, Ware 3-23, Underwood 1-18, Byham 1-3. Carolina, LaFell 5-93, Smith 5-61, Olsen 2-42, Tolbert 2-14, Stewart 1-30, Murphy 1-12.
Missed Field Goals • Carolina, Medlock 40 (WR).