LAKE FOREST, Ill. | It took a while, but Chicago Bears coach Lovie Smith eventually was able to identify a flaw Monday in the team’s 37-6 drubbing of the Seattle Seahawks.

“Devin Hester had a few problems returning punts,” Smith said after the Bears improved Sunday night to 4-0 for the first time since 1991. “If you have a rookie, you’ll go through a game like that. He’ll come back. He’s a good football player.”

And that was Smith’s confirmation that the Bears have shown very few flaws overall in compiling the best record in the NFC.

Defensively, they have been dominant. The 29 points they’ve allowed through four games is better even than their fabled 1985 defense and represents their best defensive start since 1937.

“It’s hard to score points on our defense, especially at Soldier Field,” Smith said.

The Bears have given up 13 points at home, including the only touchdown they’ve yielded defensively. The only other TD they’ve given up came from Minnesota’s defense on the road.

And third-year defensive tackle Tommie Harris twice sacked Seattle quarterback Matt Hasselbeck to bring his total to five this season, tops in the league going into Monday night’s game between Green Bay and Philadelphia.

“Tommie Harris is playing at an unbelievable level right now, just dominating football by Tommie,” Smith said. “Tommie was in the Pro Bowl last year for a reason.”

Harris’ five sacks is a single-season best, and the Bears’ 15 sacks for the season is third-best in the NFL.

“We’ve got guys who can really rush the passer,” defensive end Alex Brown said. “So if we know it’s going to be a pass, more than likely you’re in trouble.”

Offensively, quarterback Rex Grossman threw for fewer yards (232) than in any game this season. However, Smith called it Grossman’s best game so far because he made few mistakes.

“He was accurate, made all the right decisions, his numbers were good, he had a few drops in there,” Smith said.

With former Bears coach Dick Jauron bringing his Buffalo Bills to Soldier Field on Sunday, Smith sees no chance for a letdown after a big victory over one of last year’s Super Bowl teams.

“We’re 4-0 in the first quarter which is big, but no more than that,” Smith said. “Last year at this time we were 1-3 and we ended up winning the division with it. So the first quarter, the difference it really makes is hard to say. We really like the position we’re in right now but we have a long ways to go.”