CINCINNATI – Where to start with this one?

Maybe with those 51 points by a previously inept offense. Or the 554 yards by a team that had just traded its starting quarterback. That average gain of 8.8 yards for every Cleveland Browns play sure grabs the attention.

All those big numbers add up to one big – and enduring – problem for the Cincinnati Bengals. Their defense is dragging them down again.

Not even six touchdown passes by Carson Palmer were enough to get a victory Sunday in Cleveland, where the Browns’ offense did anything it wanted in a 51-45 victory that showed why the Bengals (1-1) are nothing more than a break-even team.

The defense is still broke.

“You don’t expect that to happen,” defensive captain John Thornton said Monday. “That’s why it’s so shocking.”

Shouldn’t be.

After their third 8-8 finish in coach Marvin Lewis’ four seasons, the Bengals revamped their defense, adding speed to the secondary and depth to the line. They knew that the only way they’d get back to a winning record was by getting a lot more out of a unit known for collapses.

The latest one might be the measuring stick.

The Bengals hadn’t given up so many points since a 52-31 loss to Carolina in 2002, when they finished a franchise-worst 2-14, fired coach Dick LeBeau and hired Lewis, known for running the Baltimore Ravens’ championship defense.

Lewis straightened out the team’s poor special teams, drafted quarterback Carson Palmer to get the offense rolling, and changed the franchise’s national reputation as the NFL’s Bungles.

The only thing he can’t change is the defense.

The Bengals thought they’d reached a low point in 2003, when the defense couldn’t stop Cleveland but got a late interception to seal a 58-48 victory at Paul Brown Stadium. They topped it last season by giving up 42 points in the second half of a 49-41 loss to San Diego.

Those were the Chargers. These were the Browns, who were in such disarray that they traded quarterback Charlie Frye after an opening loss to Pittsburgh. Derek Anderson, who had a total of six career touchdown passes, tied the Browns’ record with five against a defense that ranked last in the league against the pass in 2006.

The run defense wasn’t any better. Jamal Lewis ran for 216 yards, averaging 8 per carry. He had more yards on one play – a 66-yard touchdown run – than he did in nine games last season or the opening loss to Pittsburgh.

The Browns gained at least 10 yards on 19 of their 63 plays. Five passes went for at least 20 yards, while three runs totaled 30 or more.

How could that happen?

“From what we saw in film from yesterday’s game, it’s just a lot of bonehead, mental errors by us on defense,” end Bryan Robinson said. “It’s guys just being where you’re supposed to be and trusting your teammate to be where he’s supposed to be.”

They’re all on the hot seat together, along with Lewis.

“They’re put in the right spots,” Lewis said Monday, repeatedly refusing to go into detail about the defensive nightmare in Cleveland. “They just have to get it done, do it right consistently.”

Maybe. Or, maybe there’s more to it.

Now in his fifth season, Lewis stocked the defense with players who fit his mold. He took over play calling from defensive coordinator Leslie Frazier during the 2004 season, then fired him afterward and promoted current coordinator Chuck Bresnahan.

Heading into this season, all the talk was about the defense.

“I’ve been saying since training camp: If there’s a big fear for our defense, it’s the consistency level,” Robinson said. “Can we do it week in and week out?”