CINCINNATI — Cedric Benson smiled as he greeted his old Bears teammates and coaches at midfield, warmly pumping their hands or wrapping a beefy arm around their shoulder pads for a hug.

No need to rub it in. Everyone knew what he’d just done.

He got his revenge, all right.

Benson ran for a career-high 189 yards and a touchdown against the team that let him go, and Carson Palmer threw five touchdown passes — four during Cincinnati’s dominant first half — in a shocking 45-10 victory Sunday that will go down as one of the worst days in Bears history.

‘‘Everybody knew it was going to be an emotional day,’’ said Benson, who spent two turmoil-filled seasons in Chicago. ‘‘Everybody knew. What a wonderful day and a wonderful thing, to go out there and strut your stuff.’’

All around, there was strut in their stride.

The Bengals improved to 5-2 for the first time since 2005, when a fast-strike offense got them to the playoffs. There was a strong resemblance in the first half, when Cincinnati scored on all five possessions and went up 31-0. It tied for the third-most points the Bears (3-3) have allowed in an opening half.

In that half alone, Chad Ochocinco had 103 yards receiving and Benson had 98 yards rushing as the Bears gave up more points than they had in any game all season. Palmer finished 20 of 24 for 233 yards, one shy of his career high for touchdown throws.

‘‘I don’t understand why it went this way today and why it didn’t go that way last week or the week before that,’’ said Ochocinco, who had 10 catches for 118 yards and two touchdowns. ‘‘The offensive line played unbelievable. For Ced to run the way he did today and for us to be able to throw, we could have done what we wanted to do.’’

Something wasn’t right on Chicago’s reshuffled defense.

The Bears have constantly rearranged their linebackers because of injuries, including Brian Urlacher’s dislocated right wrist. Middle linebacker Hunter Hillenmeyer moved outside Sunday in the latest revamping, and the line was missing tackle Tommie Harris.

Even with that, it was hard to explain.

‘‘That was pretty embarrassing,’’ defensive end Alex Brown said. ‘‘It’s embarrassing to come out and play like that. I tip my hat to their whole team. Cedric ran the ball like crazy. They did whatever they wanted to do.’’

Especially No. 32.

The focus was on Benson, who was Chicago’s top draft pick in 2005 but couldn’t crack the starting lineup for long or earn a spot in some of his teammates’ hearts. They let him go after two stormy years, and the Bengals signed him last season.

Carrying a grudge, he played like a No. 1 pick.

Benson ran for 32 yards on the Bengals’ opening drive, even taking a direct snap in the wildcat formation. Lowering his shoulder for extra yards, he topped 100 in the half, before a loss dropped him down. After his 1-yard touchdown run made it 45-3, he merely flipped the ball aside.

‘‘He wanted to get back at us,’’ Bears safety Danieal Manning said. ‘‘We expected that, and would expect nothing less.’’

Benson was so inspired that he got a little too excited early in the game.

‘‘There were a few times where I may have gotten a little too hyped up, a little too antsy,’’ he said. ‘‘A couple of drives, I found myself having to calm myself down and gather my emotions to stay poised. Once I got past that, we were good to go. Keep it rolling.’’

It quickly became a wrecking job, one so complete that Benson could be magnanimous.

‘‘I continue to be as graceful as I can be,’’ he said. ‘‘I’m not shoving anything in anybody’s face. Like I say, it wasn’t a revenge day for me. I just wanted to take advantage of the opportunities.’’

While Benson did the bruising work, Palmer — playing with a brace on his sprained left (non-throwing) thumb for the second straight week — piled up the points. Palmer threw short touchdown passes to different receivers on the first four drives.

Chicago hadn’t given up so many first-half points since 2003.

Forced to throw, Jay Cutler had a tough time against a Bengals defense missing its best pass rusher. Antwan Odom had surgery last week for a torn Achilles’ tendon. In its first game without him, Cincinnati barely missed him.

Cutler got a two-year extension last week through the 2013 season, an extra $20 million guaranteed as a sign of the Bears’ faith. In his first game since the show of confidence, Cutler threw three interceptions, fumbled two snaps and finished 26 of 37 for 251 yards.

NOTES: It was Chicago’s most lopsided loss since a 49-7 defeat at San Francisco in the first game of 2003. … The Bears’ record for most points allowed in a first half is 34 at Baltimore on Oct. 4, 1958. They gave up 33 in the first half of that 49-7 loss to San Francisco in 2003. They’ve given up 31 points four times. … Palmer threw six touchdown passes in Cleveland for his career high. … It was Cincinnati’s most lopsided win since a 38-3 victory over the Texans in 2002.

Bengals’ stats

Chicago 0 3 0 7 — 10

Cincinnati 14 17 7 7 — 45

First Quarter

Cin—Henry 9 pass from C.Palmer (Graham kick), 11:00.

Cin—Ochocinco 8 pass from C.Palmer (Graham kick), 1:07.

Second Quarter

Cin—Foschi 3 pass from C.Palmer (Graham kick), 11:14.

Cin—Coles 8 pass from C.Palmer (Graham kick), 2:49.

Cin—FG Graham 29, 1:10.

Chi—FG Gould 22, :00.

Third Quarter

Cin—Ochocinco 13 pass from C.Palmer (Graham kick), 4:48.

Fourth Quarter

Cin—Benson 1 run (Graham kick), 14:57.

Chi—Hester 5 pass from Cutler (Gould kick), 11:48.

A—64,900.

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Cin Chi

First downs 15 30

Total NetYards 279 448

Rushes-yards 12-35 45-215

Passing 244 233

Punt Returns 0-0 0-0

Kickoff Returns 7-151 2-35

Interceptions Ret. 0-0 3-68

Comp-Att-Int 27-39-3 20-24-0

Sacked-Yards Lost 1-10 0-0

Punts 3-39.0 1-36.0

Fumbles-Lost 3-1 0-0

Penalties-Yards 6-44 3-20

Time of Possession 23:38 36:22

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INDIVIDUAL STATISTICS

RUSHING—Chicago, Forte 6-24, Wolfe 3-7, Cutler 3-4. Cincinnati, Benson 37-189, Scott 6-17, O’Sullivan 2-9.

PASSING—Chicago, Cutler 26-37-3-251, Hanie 1-2-0-3. Cincinnati, C.Palmer 20-24-0-233.

RECEIVING—Chicago, Hester 8-101, Bennett 4-48, Knox 4-42, Forte 4-25, Olsen 4-24, Clark 3-14. Cincinnati, Ochocinco 10-118, Coles 2-37, Henry 2-26, Caldwell 2-19, J.Johnson 2-16, Scott 1-14, Foschi 1-3.

MISSED FIELD GOALS—None.