The first-half storyline for the Illini on Saturday was an unfamiliar one.

Riding a strong performance by an injury-marred defensive secondary and a productive running game on offense, Illinois headed into halftime with a 13-3 advantage against Missouri. The 10-point lead was the highest advantage the Illini has held in the six years of the Arch Rivalry series, and also marked the first time Illinois led at halftime.

The second half, though, was a different story.

Illinois managed only four first downs after halftime, and Missouri outscored Illinois 20-0 in the second half to win the final game of the Arch Rivalry series, 23-13.

“It was a tale of two halves,” Illinois head coach Ron Zook said. “In the first half we played well, and we began to lose it right there in the first five minutes of the third quarter.”

After gaining 196 total yards of offense in the first half, the Illini netted 85 in the second half. The Missouri offense, on the other hand, gained 242 second-half yards after a 137-yard performance in the first half.

“You have to give Missouri credit,” Zook said. “They came out and played well on offense and defense (in the second half), and we came out and kind of stumbled around in the third quarter.”

The differing levels of intensity between the two teams, Zook said, was the main factor behind Missouri’s second-half rally.

“They raised their level, and we didn’t maintain our level,” Zook said.

The Illini defense, without starting cornerback Terry Hawthorne (right foot stress fracture) and safety Supo Sanni (ruptured Achilles tendon), held its own against Missouri quarterback Blaine Gabbert and the Tiger offense in the first half, holding the passing attack to 114 yards and no touchdowns. But Gabbert went on to complete 20 of 28 passes for 167 yards in the second half, including two touchdown passes.

“Football’s a 60-minute game, and we’ve got to learn all 60 minutes,” defensive coordinator Vic Koenning said. “We’ve just got to be electric and fast tempo all the time. Defense is either all-go or you don’t. There’s no in-between.”

Saturday’s game marked the collegiate debut of redshirt freshman quarterback Nathan Scheelhaase, who finished with 81 passing yards on 9 of 23 passing as well as 76 yards on the ground. He found junior receiver A.J. Jenkins for a 13-yard touchdown in the second quarter and engineered a 34-yard drive with 45 seconds left in the first half to set up a 52-yard field goal by Derek Dimke.

But Scheelhaase finished the game with three interceptions and a fumble and was sacked twice in the game.

“Obviously it was not the kind of game he would have liked to have had,” Zook said. “But I feel very, very good about Nathan. One of the things that I’ve said all along is that Nathan will learn from his mistakes. Some of the things that maybe didn’t go the way you want, it was because he was trying too hard. He’ll learn from that and get better and better.”

The Illinois offense sputtered in the second half, gaining a total of 10 yards in the third quarter, including consecutive three-and-outs. Two of Scheelhaase’s three interceptions came in the second half.

“It’s frustrating when we stall like that and definitely for myself there were plays to be made,” Scheelhaase said. “Some of those plays that were there to be made, we didn’t make them and I didn’t make them. We’ve got to play 60 minutes of football to win games.”

Even with the loss, both players and coaches acknowledged the boost in confidence for the team after its first-half performance.

“Other than the loss, there are an awful lot of good things to work on and to get better from,” Zook said.

The Illini offense generated 200 yards on the ground. Junior running back Mikel Leshoure netted 112 rushing yards on 20 carries, including a 42-yard scamper in the second quarter that helped set up the team’s only touchdown.

“You’re judged on wins and losses,” Zook said, “but I know this — I am very optimistic about the season.”