Can you really say there was a "turning point" to a game when it felt like more watching the long, slow grind of continental drift? For the better part of three hours this game was watching two fairly hapless offenses smash against the same brick walls again and again and again. The Iowa offense managed to make few more dents in that wall as the game went along and finally broke a hole in the wall late in the fourth quarter.
In terms of win percentage, the play that had the most impact for Iowa was Nate Stanley's 30-yard pass to Brandon Smith on 3rd and 4 from the ISU 32-yard line with five minutes to go in the game. Iowa led 6-3 at that point but getting a touchdown on that drive would give them a 10-point lead, which would have been basically insurmountable, given the time remaining in the game and the way Iowa's defense had been playing. (And, indeed, that's exactly what happened.) Iowa's win percentage before the Smith catch was around 69% (nice); after Smith's catch the win percentage shot up to 89.4%. (It went to 99% after Mekhi Sargent ran for a touchdown a play later.) So yeah: Smith's catch took the game from a likely Iowa win to an almost sure thing. That seems like a big deal!
But I think the real turning point for the game was the Iowa defense putting the Iowa State offense on lockdown. Once the defense got going, Iowa State's offense looked helpless and it was just a matter of Iowa's own offense finding a way to score enough points to win the game. That took a while because Iowa's offense also looked very helpless (and hapless) for much of the game and in a close game there's always the risk of a big, fluky play having an outsize impact on the outcome of the game, but still -- once it became clear how well Iowa's defense was playing, I felt much more confident about their ability to win this game.
Iowa was excellent after ISU's opening drive, which was the only time they scored points all day. After that drive (13 plays, 66 yards, 3 points), ISU managed just 43 plays and 122 yards. They had four first downs on that opening drive -- and just seven first downs the rest of the game. They averaged 5.1 yards per play on the opening drive and just 2.8 yards per play for the rest of the game. They crossed midfield just once after that opening drive and never got back into the red zone. The Iowa defense absolutely put shackles on the Iowa State offense after the first drive and barely let them move.
I would argue that their clamp-down really came slightly earlier, too -- during that aforementioned opening drive. Iowa State had first and goal from the Iowa 2-yard line -- and ended up settling for a field goal. Iowa stuffed a completed pass to TE Dylan Soehner short of the end zone on first down, then held David Montgomery to a one-yard gain on a second down run. After an incomplete pass on third down made it fourth and goal from the Iowa 1-yard line, Iowa State was going to go for it -- until the defense (with an assist from the very loud Kinnick crowd) forced ISU into a false start penalty that knocked them back five yards.
That goal line stand ended up being a huge moment in the game. Obviously in a game where points ended up being at such a premium, holding ISU to three points instead of seven was a big deal. It was also a huge confidence boost for the Iowa defense -- after getting pushed around and moved on with ease by ISU's offense in getting down to the Iowa 2-yard line, they stiffened and kept them out of the end zone. They were able to carry over that same level of lockdown defense to the rest of the game and that was all she wrote for ISU's chances in the game.