AMES, Iowa (AP) -- Iowa State finally played well enough to give Kansas State a scare.

	Iowa State's Jesse Beckom sacks Kansas State quarterback Jonathan Beasley.

Down 28-7 at halftime, No. 15 Kansas State rallied in the second half on David Allen's 94-yard punt return and No. 2 quarterback Adam Helm's steady play to beat Iowa State 35-28 Saturday.

The Wildcats (3-0) didn't lead in the Big 12 opener until Helm scored the winning touchdown on a 1-yard run with just 2:34 left, capping the biggest comeback in Bill Snyder's 11 seasons as coach.

"We were lucky enough to pull it together in the second half," Kansas State linebacker Travis Litton said. "We made up our minds that we were not going to give up and we knew if we limited our mistakes, we could win the ball game."

The Wildcats did, though only after Iowa State (3-1) dominated the first half, outgaining Kansas State 332-102 and looking nothing like the team that has lost the previous five games in the series by an average of 29 points.

The Kansas State defense stiffened and Helm revived a sputtering offense after replacing starter Jonathan Beasley on the second series of the third quarter.

"When you have them down, you've got to push them over the cliff," Iowa State offensive tackle Bill Marsau said. "You can't let them back in it and we did."

A key for the Wildcats was getting Iowa State's Darren Davis, the nation's No. 2 rusher, under control. Davis carried 17 times for 131 yards in the first half, then was limited to 21 yards in nine second-half carries.

Iowa State, which had been leading the nation in rushing, managed only 74 total yards over the final two quarters.

"In the first half, I was just stunned how they were moving the ball," Kansas State safety Lamar Chapman said. "Then we just started playing hard."

Helm, who scored twice on short runs, led touchdown drives of 80, 75 and 62 yards as the Wildcats went to a short passing game that moved the ball and also opened the running game.

A 2-yard touchdown run by Helm drew Kansas State to 28-14 late in the third quarter and Allen silenced the Iowa State crowd with his punt return 3½ minutes later.

Catching the ball at his 6, Allen started left then turned straight upfield. Once he eluded a futile dive by punter Carl Gomez at midfield, Allen was home free. It was his sixth career punt return for a touchdown, one short of the NCAA record, and matched the longest in school history.

Chapman ran back a punt 94 yards against Ohio University in 1997.

"It was a great effort on David's part," Snyder said. "That's what we try to convey to our punt return team -- if they stay on their blocks for a while, you've got a guy back there who can do some good things."

Iowa State safety Jeff Waters, on the sideline at the time, said Allen had some help.

"I saw a clip in the back," Waters said. "A lot of our guys were yelling, 'Clip, clip.' But officials are human, too. That was a big play for them. It gave them momentum and they carried it over."

Frank Murphy's 18-yard run and Jamie Rheem's extra point tied it at 28 with 10:01 remaining, and the Wildcats got the ball right back after the defense forced yet another punt.

This time, Helm took his team 62 yards in 11 plays, finishing the drive with a keeper. Kansas State's biggest comeback previously under Snyder had been from a 14-point deficit in a 23-21 victory over Cincinnati in 1995.

Helm finished 7-of-11 for 67 yards and ran 13 times for 48 yards.

Kansas State spent the first half watching Iowa State move up and down the field with a variety of fakes, reverses, option plays, handoffs to Davis and quick passes to the tight end, who often was left uncovered.

Davis scored on runs of 26 and 10 yards and left a succession of would-be tacklers on the ground grasping nothing but air. In the second half, however, those tacklers brought him down.

"Their defense played outstanding," Iowa State coach Dan McCarney said. "The longer the fourth quarter got, the better they got. We might not have scored no matter how long we played in the second half."