IOWA CITY, Iowa (AP) There was legitimate cause for concern regarding Iowa's revamped defense heading into 2015.

The Hawkeyes answered their critics with a largely brilliant start to the season: Iowa stymied Illinois State, allowing zero points and just 79 yards through three quarters of a 31-14 win last weekend.

The Hawkeyes picked up five sacks and didn't let the Redbirds reach their 20-yard line until their backups allowed a pair of late touchdowns by the FCS team.

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Iowa (1-0) will hope for a similar performance in a much tougher spot on Saturday when it travels to face Iowa State (1-0).

''We went back to the drawing board and really looked at last year, and the things that we got caught up on were the little things,'' linebacker Travis Perry said. ''We just went back and tried to correct the little things and I think we did a pretty good job.''

The Hawkeyes lost a pair of star tackles to graduation and brought back a group of linebackers who looked terrible at times in 2014.

That's why the domination their front seven showed against Illinois State and its talented backfield was such a surprisingly positive development.

Senior end Drew Ott, the only real certainty along Iowa's line, was predictably disruptive with a pair of sacks and a forced fumble. But 310-pound junior Jaleel Johnson consistently broke into the backfield in his first career start. Illinois State running back Marshaun Coprich, a first-team All-America pick last season, ran for just 32 yards - 119 below his average from 2014 - on 13 carries.

The Hawkeyes' ability to contain outside runs, which Ott called a ''dagger in our backs'' last season, was largely exceptional in the opener.

Iowa was burned on multiple occasions outside in a ghastly bowl loss to Tennessee in January. But the starting trio of Ben Neimann, Josey Jewell and Cole Fisher helped hold Illinois State quarterback Tre Roberson, an Indiana transfer who had 4,250 yards of offense in 2014, to just 49 yards passing and minus-12 yards rushing.

Illinois State ran just 55 plays, and 10 of those ended with a Redbird tackled behind the line of scrimmage.

''When you get that kind of penetration from the line, it just makes all the reads from the linebackers 10 times easier. They helped out tremendously,'' Fisher said.

It wasn't a perfect game from Iowa's defense. The fact that Illinois State was able to string together back-to-back touchdown drives against Iowa's backups had to concern coach Kirk Ferentz - especially if starters start going down with injuries.

But as far as debuts go, Iowa's defense couldn't have asked for a better one.

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Online: AP College Football website: www.collegefootball.ap.org