Running back Doug Martin took over the NFL rushing lead for the Bucs, but his two fumbles were huge in shifting momentum to the Bears, who got a second-quarter field goal off the first fumble and a touchdown on the first play of the fourth quarter off the second.
Chicago (6-9) received strong running - and zero fumbles - from Jeremy Langford and Matt Forte in handing the Bucs (6-9) their third straight loss. The Bears' backfield tandem combined for 137 yards on the ground.
"It's one of the more critical statistics other than winning and losing," Bears coach John Fox said of his team's plus-three turnover margin. "I think all of them were rookies. Jonathan Anderson was responsible for one, (John) Timu recovered two of them and then Harold Jones-Quartey had the one interception that was key. Those are always big, and to be on that side of the turnover margin helped us win today."
Lovie Smith lost to his old team for the second time in as many seasons.
The Bucs got a touchdown with one second left as rookie quarterback Jameis Winston hit tight end Austin Seferian-Jenkins for a 43-yard score.
"I thought we would play a lot better than we did today," Smith said. "It's tough to win when you do some of the things we did out there - turnovers, starting with that. I thought we were prepared, but normally you have a loss when you play like that."
The Bears took the lead on Jay Cutler's 1-yard throw to running back Ka'Deem Carey on the first play of the fourth and would add a field goal.
Winston, whose 50-yard touchdown pass had given the Bucs a 14-13 lead in the third quarter, twice got inside the Chicago 25-yard line without scoring.
His third-down interception from the 12 killed one drive, and the Bucs were at the 24 in the fourth quarter when a snap rolled low past Winston for a 10-yard loss, setting up a missed field goal from 52 yards to keep it a two-score game.
Robbie Gould had four field goals for Chicago, including a 50-yarder in the fourth quarter. The Bears eclipsed last year's win total with the victory.
"We feel it. Those guys feel it," Fox said. "We're getting there. We need to improve. They're still trying to finish this year well and we've got one more game to try to avoid a double-digit losing season."
The Bucs' only scoring in the first half came off a blocked punt by linebacker Jeremiah George, with the loose ball recovered at the 4, setting up a Martin touchdown on the next play. The Bears answered for a 10-7 halftime lead, converting two Tampa Bay penalties on their touchdown drive and a Martin fumble into the go-ahead field goal.
"It feels like a bad dream right now," Martin said. "That's out of character for me to fumble the ball twice in one game. I'm embarrassed. I feel like I let the team down."
NOTES: Bears WR Alshon Jeffery was inactive after catching just one pass last week. ... The Bears were already without TE Martellus Bennett (injured reserve). With Jeffery out, the rest of the Bears' receivers have a total of three touchdown catches this season. Backup Josh Bellamy started in Jeffery's place. ... Bucs S Chris Conte missed his first game of the season with a knee injury. Keith Tandy started in his place. Tandy has worked at safety and nickel defensive back this season. ... Bucs WR Vincent Jackson (knee) and backup defensive end Kourtnei Brown (groin) missed Sunday's game.