CARBONDALE, Ill. -- Southeast Missouri State probably has had bigger wins during its long football history.

But the stunner that took place here Saturday night unquestionably is the program's biggest victory under fifth-year coach Tony Samuel.

In a result that will send shock waves throughout the Division I-AA football world, Southeast rallied from an 18-point second-half deficit to upset fifth-ranked Southern Illinois 24-21.

"They're No. 5 in the nation. Nobody expected that, other than the people in our locker room," Samuel said. "Great win for the program. We've struggled. It's great to accomplish what we accomplished."

An announced crowd of 13,078 at brand-new, $25 million Saluki Stadium saw Southeast improve to 2-1 while dropping SIU to 1-2.

Southeast Missouri State's Henry Harris scores the winning touchdown against Southern Illinois Saturday, Sept. 18, 2010 at Carbondale, Ill. (Fred Lynch)

The Redhawks, in beating a top-five opponent for the first time since moving up to Division I-AA in 1991, have matched their win total from last season.

"It's just electrifying right now," said junior wide receiver Chantae Ahamefule, who caught seven passes for 94 yards. "I'm speechless, out of breath. We fought hard for four quarters."

Senior tailback Henry Harris, who rushed for a career-high 142 yards on 17 carries, scored the winning touchdown when he broke off a 67-yarder with 3 minutes, 41 seconds remaining in the game.

"Right now it feels so good, I don't have any emotion," Harris said. "Coach Sam kept believing in us and we just kept fighting.

"Even after this win, I'm sure we'll have a lot of doubters, but we believe."

Southeast Missouri State's Henry Harris runs for the winning touchdown while Southern Illinois' E.J. Clark tries unsuccessfully to keep up during the fourth quarter Saturday in Carbondale, Ill. (Fred Lynch)

It was understandable that so many people doubted the Redhawks could beat the Salukis.

For starters, Southeast had not even come close to SIU since the Salukis became a Division I-AA powerhouse, losing the past four meetings by a combined 170-57.

That includes last year's 42-24 defeat in Cape Girardeau that marked Southeast's first matchup with SIU since Samuel took over the program.

Throw in the fact that the Redhawks trailed 21-3 with less than a minute left in the third quarter, and an upset seemed even more improbable.

"We just never quit," junior linebacker Philip Klaproth said. "Don't give up. We can't be beat, we won't be beat, that's our motto.

"It feels amazing, to finally show people what we're about, what we're capable of doing."

Southeast handed SIU its first nonconference home loss since 2002 -- which ironically was administered by Southeast, 21-14, as the then-Indians notched their most recent win over SIU.

"Unbelievable, especially the way we did it," said junior quarterback Matt Scheible, who completed 12 of 19 passes for 163 yards and did not throw an interception for the sixth straight game. "Coach Samuel always preaches playing four quarters. We did it.

"This shows we can handle adversity. We train for this."

Although Southeast grabbed a 3-0 lead late in the first quarter, SIU went ahead 14-3 at halftime. The Salukis expanded the margin to 21-3 late in the third period.

But Southeast's defense held SIU scoreless the rest of the way and the Redhawks' offense, which had been up and down, suddenly gained consistency.

Southeast answered SIU's touchdown that made it 21-3 by driving 71 yards, the key play being a 39-yard pass from Scheible to the 6-foot-6 Ahamefule, who carried it to the SIU 3-yard line.

Senior tailback Mike Jones' 1-yard run with 42 seconds left in the third quarter cut the deficit to 21-10 -- and had Samuel feeling positive.

"We struggled a little bit in the third quarter, but with 42 seconds left in the third quarter I felt good about our team," Samuel said.

SIU was forced to punt, and Southeast drove 74 yards, capped by a 14-yard touchdown run from Harris with 8:22 remaining. All of a sudden it was 21-17.

After another SIU punt, Southeast's offense put together its third straight scoring drive, this time a 75-yarder that required only three plays.

On third-and-2 from the 33, Harris found a big hole up the middle, then outran a final defender to the end zone to make it 24-21 Southeast with 3:41 left.

"It felt great," Harris said. "It was an excellent play call and great blocking."

SIU still had a shot, but again Southeast's defense came up big.

Klaproth sacked quarterback Chris Dieker for a 4-yard loss on first down. On third-and-14, sophomore safety Tylor Brock came up with his first collegiate interception on a deflected pass that he said was tipped by sophomore linebacker Darrick Borum.

"Good timing," Brock said of his pick, then added of the win, "It's amazing. I've never felt anything like that in my life."

Taking over at the SIU 36 with 2:59 left, Southeast picked up two first downs and then was able to run out the clock with three Scheible kneel-downs.

"It's an amazing feeling. It doesn't get any better than this," fifth-year senior linebacker Joshua Jackson said. "This has got to be the biggest win since I've been here."

As the final horn sounded, the Redhawks celebrated on the field and then ran toward the approximately 300 Southeast fans in attendance to show their appreciation.

"We could hear them the entire game," Samuel said. "I don't usually hear the fans when I'm coaching, but I heard them tonight."