Losing their third straight game for the first time under Mike Ditka, the Bears fell victim to a club-record 98-yard touchdown pass play from Bernie Kosar to Webster Slaughter in the fourth period.
The loss dropped the Bears (4-3) out of first place in the National Football Conference Central Division for the first time since the end of the 1983 season.
"Maybe we have to go back to establishing the run," Ditka said after the game. "We're going to go back to the drawing board. Their rush really took us out of sync.
"'I thought our (defensive) kids played pretty good. The best we've played defensively.
"There were a log of good things out there a lot of bad things."
The Bears are 2-14 in Monday night road games.
Meanwhile, the Browns (4-3) moved into a tie with Cincinnati and Houston for first in the American Football Conference Central Division.
The Bears' only score came on a 5-yard pass from Jim Harbaugh to Wendell Davis with 3 minutes 47 seconds left in the game. Harbaugh relieved an ineffective Mike Tomczak in the third period.
The Browns enjoyed a 7-0 lead at halftime as the Bears were held scoreless in the first half for the first time since Dec. 14, 1987, when the San Francisco 49ers went on to wallop them 41-0.
Kosar completed 7 of 8 passes, including four in a row, as the Browns marched 73 yards in 14 plays to take a 7-0 lead late in the first quarter.
Kosar's 3-yard touchdown pass to Eric Metcalf capped the drive as the rookie made the grab in front of linebacker Ron Rivera on a crossing pattern. The Browns had seven first downs to the Bears' one in the first period.
Cleveland expanded its lead to 10-0 in the third quarter on a 31-yard field goal by Matt Bahr after a 72-yard drive that featured passes of 20 and 27 yards from Kosar to Slaughter (8 catches, 186 yards).
Frank Minnifield intercepted a Tomczak pass with 6:01 left in the third to set the Browns up at the 25.
Following a 12-yard pass to tight end Ozzie Newsome and a 7-yard pass to Slaughter, Metcalf darted 7 yards for his second touchdown of the night and a 17-0 Browns lead.
After completing only 4 of 14 passes for 76 yards and one interception, Tomczak, celebrating his 27th birthday, was yanked in favor of Harbaugh with 4:25 left in the third.
Richard Dent (bruised thigh), who didn't practice last week, was one of the Bears' two inactive players. Rookie John Shannon started in Dent's place at right end and rookie Tony Woods made his second NFL start at left end in place of Trace Armstrong.
Armstrong, recovering from a severe ankle sprain, did enter the game later in the first half.
"My ankle is coming along pretty fast," said Armstrong. "I think I've surprised a lot of people. I think the biggest key to healing is wanting to come back and seeing yourself get healthy."
Woods managed a first-half sack of Kosar. And the Browns' Michael Dean Perry, brother of the Bears' William "the Refrigerator" Perry, sacked the Bears' Tomczak.
In last Sunday's 33-28 loss to the Oilers, the Bears' defense had no sacks.
"We probably don't have as great a guys blitzing as we did have," said Bears defensive coordinator Vince Tobin of the injuries to the starters. "And I think also that offenses are a lot more intelligent on how to pick up blitzes and how to react to blitzes. This has been the trend for the last two or three years. That has been the trend all through the league.
"Whether you do or don't have a pass rush, I think you have to do different things. You've still got to put doubt in the quarterback's mind about whether you're playing man or whether you're playing zone or whether you're blitzing."
There was talk early last week that the Bears might try to simplify their defense to accommodate the high number of rookies and free agents.
"We haven't simplified it," said Ditka. "We changed some things, but we haven't simplified it. You simplify it and they will blow you right out of the stadium. There can be nothing simpler than three-deep zone. That's the basic defense of pro football. It's the first thing you learn in high school. When you can't play that very well, then you have to look at the individual playing that position."
Both the Bears and Browns were coming off two-game losing streaks.
"To me, every week is a must-win," said Bears middle linebacker Mike Singletary.
"We shouldn't have lost two in a row, but we did," said Ditka.
The Bears and Browns combined for 13 turnovers in losses to Houston and Pittsburgh, respectively, last week. But there were no turnovers by either team in the first half.
Kosar completed 12 of 17 passes in the first half for 85 yards. Tomczak, who had genuine respect for the Browns' defense before the game, was only 3 of 11 for 53 yards in the half.
"The Browns have two corners-Frank Minnifield and Hanford Dixon-who can play man-to-man the whole game and (linebacker) Clay Matthews is probably playing the best he has ever played in his career," said Tomczak.
Cornerback Lorenzo Lynch started in place of Vestee Jackson, who missed three practices last week. Kosar picked on Lynch by hitting Slaughter for four passes for 35 yards in the first half. Jackson was Slaughter's victim on the 98-yarder.
"(Lynch) tries," said Ditka. "He has played part of the time for us and he has had three interceptions. Something has to go right to get three interceptions. You've got to be working and you've got to be thinking. I know that when he is out there he will give us the best he's got."
Both Kosar and Tomczak had subpar games last Sunday, throwing four interceptions apiece.
"I don't like to see anybody have a slump," said Ditka before the game. "I anguished when (Cubs outfielder) Andre (Dawson) had a slump. I don't like to see Arnold Palmer have a slump. I don't like to see any slumps at all. I like to see guys perform.
"Bernie Kosar I don't think he has to apologize to anybody. I think he is top drawer. Quality. He's one of the top quarterbacks in the league."