COLUMBUS, Ohio – Ohio State was supposed to be in transition, replacing a Heisman Trophy winner, a couple first-round draft picks and numerous key players from a team that played for a national championship last season.

Now the rebuilt Buckeyes are No. 1 in the AP Top 25 and the Bowl Championship Series standings thanks to a string of surprising results over the past three weeks. The final unlikely events unfolded Saturday when the top two teams in the rankings – LSU and California – both lost and the door to the top spot swung open for the unbeaten Buckeyes.

“Our guys have done what they have needed to do to this point in the year, and we are pleased with that effort and progress, but not content,” Ohio State coach Jim Tressel said Sunday. “With the most demanding part of our schedule remaining with five Big Ten Conference games, there is a lot of work ahead of us. We’ve improved each week, but we understand that the only poll that counts is the last one.”

The Buckeyes host Michigan State on Saturday, then go to Penn State, have Wisconsin and Illinois at home and finish up at Michigan.

“It’s an honor to be considered among the top teams in the country, but it doesn’t mean anything until the last game of the season,” linebacker and captain James Laurinaitis said. “We found that out last year. We need to focus and take care of Michigan State and the work ahead of us in the Big Ten.”

The Buckeyes’ top ranked defense is credited for their unexpected success this fall.

Ohio State was No. 1 all season in 2006, then lost the national title game to Florida and finished No. 2.The Buckeyes have rolled through their first seven games on the strength of the nation’s best defense. Led by Laurinaitis, fellow linebacker Marcus Freeman and stout lineman Vernon Gholston, Ohio State is allowing only 6.6 points and 212 yards per game.

The quality of the Buckeyes’ competition has been sketchy. They’ve beaten three overmatched teams from Ohio – Youngstown State, Akron and Kent State, won at Washington and swept by Northwestern, Minnesota and Purdue in the Big Ten.

But while so many highly ranked teams have slipped against underdogs, the Buckeyes just keep winning – even with much of their offensive firepower from last season in the NFL.

Heisman-winning quarterback Troy Smith, tailback Antonio Pittman and wide receivers and kick returners Ted Ginn Jr. and Anthony Gonzalez were all capable of turning a small defensive mistake into a touchdown.

Still, the big play remains a big part of Ohio State’s game, with first-year starting quarterback Todd Boeckman directing the offense and running back Chris Wells providing muscle and speed.

The Buckeyes have had 43 plays of 20 or more yards. Those long gainers did most of the damage in Ohio State’s 48-3 victory over Kent State on Saturday.

With the Buckeyes holding a 7-0 lead early in the second quarter, Kent State was forced to punt on fourth-and-16 at the Ohio State 47. Jake Kilroy’s punt went to Brian Hartline at the 10, where he pivoted and then raced to the right sideline.

Kent State’s Kirk Belgrave had a clean shot at Hartline but stumbled and fell.

Once Hartline turned the corner, no one came close to tackling him.

“It’s not a single-man thing,” Hartline said. “There is lots of dirty work being done.”

The return erased the Ohio State record of 87 yards set by Robert Demmel in 1950 against Iowa.

Later in the second quarter, Kent State faced a second-and-3 at the Ohio State 35 when Julian Edelman took a three-step drop and threw toward the right sideline for wide receiver Phil Garner.

Edelman’s pass was slightly underthrown and behind Garner, with cornerback Donald Washington picking it off and racing 70 yards for the score to make it 28-0.

“You get all those people cheering – and you’re doing something great for the team – and that’s a dream come true,” Washington said.

Sort of like being No. 1 in a rebuilding year.