In today's SB Tribune, Lenzy is quoted as saying he was completely gassed in the 2nd half due to having to run so many fly routes well above the norm. He said at one point he tried to remove himself from the game because he was unable to run routes at full steam but Del turned him back onto the field, telling him there would be no substituting. I doubt that was Del's decision. That falls on TR. At some point, he should have realized he had to run the ball more just to give his receivers a breather and he needed to substitute more by giving Colzie more reps and Thomas any reps at all. You can read about it
here (it's behind a paywall).
And if anyone saw the most recent Inside the Garage Podcast, Cam basically said the defense collapsed because they weren't ready for the speed of OSU uptempo offense. He said they practiced against uptempo, but OSU was running a hyper version they weren't prepared for.
So by the 4th quarter, they had a double whammy of both the O and D gassing.