GREEN BAY, Wis. – The Green Bay Packers coughed up five turnovers and their chance to remain undefeated, blowing a second-half lead and handing a 27-20 victory to the Chicago Bears at Lambeau Field Sunday night.

Bears quarterback Brian Griese threw the go-ahead touchdown to tight end Desmond Clark with 2:05 left. Brett Favre drove the Packers to the Bears 31 and called the Packers’ final timeout with 13 seconds remaining, but Favre threw an incomplete pass and an interception to Bears safety Brandon McGowan in the end zone to end the game.

Favre had marched the Packers (4-1) up and down the field in the first half, shredding a Chicago defense that continued to look nothing like the unit that led the Bears (2-3) to the Super Bowl last season.

But the old Favre reared his ugly head late in the third quarter when he threw a head-scratching interception to Bears linebacker Brian Urlacher that let Chicago back into the game.

Griese made the Packers pay for Favre’s mistake right away, throwing a 19-yard touchdown pass to rookie tight end Greg Olsen to cut the Packers’ lead to 20-17 with 4:19 left in the third quarter. Olsen caught the pass out of bounds, but officials ruled he had been pushed out by Packers safety Atari Bigby, a call that is not subject to replay review.

Green Bay held Chicago on its next possession, but the Packers’ Charles Woodson fumbled on a punt return to give the ball back to the Bears at the Green Bay 41. Chicago drove for a 36-yard field goal by Robbie Gould, tying the game with 14:13 remaining.

The teams traded defensive stops deep into the fourth quarter, when the Bears appeared to convert a third-and-4 at the Packers 42 with 3:13 remaining. Packers coach Mike McCarthy challenged the spot and got the ball moved, just not enough to take away the first down.

After a 7-yard run by Cedric Benson, the Bears faced third-and-2 at the Packers 34, Griese faked a handoff and threw down the seam to Clark, who had broken free from safety Nick Collins and linebacker Brady Poppinga. Clark ran to the end zone, giving the Bears a 27-20 lead.

Griese, playing his second game as the Bears’ starter after Rex Grossman was benched, finished the game 15-of-25 for 214 yards with two touchdowns and one interception.

Favre was 29-of-40 for 322 yards with a touchdown and two interceptions, tying George Blanda’s record of 277 career interceptions.

Favre threw for 243 yards in the first halfand the Packers led 17-7 at halftime despite two first-quarter fumbles by rookie receiver James Jones in Bears territory.

The Packers drove 83 yards on their first possession, scoring on a 2-yard run by rookie DeShawn Wynn. Wynn set up the touchdown with a 44-yard burst up the middle earlier in the drive, the longest rushing play of the season for what has been a dormant Packers running game.

After a three-and-out by the Bears’ offense, the Packers drove deep into Bears territory until Jonescaught a pass and was stripped by Bears cornerback Charles Tillman on Chicago’s 16.

The Packers drove back into Chicago territory, only to have Jones again stripped by Tillman.

Chicago didn’t get a first down until the 13:05 mark in the second quarter, finally putting together a drive that ended with a 10-yard touchdown run by Cedric Benson to tie the game.

Favre answered on the Packers’ next possession, rearing back for a 41-yard touchdown pass to Greg Jennings. The Packers added a 37-yard field goal by rookie Mason Crosby just before halftime, taking a 17-7 lead into the locker room.