That punch would have put most fighters to sleep and we have to remember Khan didn't force the Rehydration clause which was suicidal, i read today that Canelo was a little over 180 pounds and even said no when HBO asked to weigh him just before the fight, that's a MASSIVE advantage that Amir gave him and a foolish one. I actually thought he was in serious trouble when he hit the canvas then noticed his chest moving and realised he was at least breathing.
Canelo landed a few hard body shots that Khan tried to grin off which is a tell tale sign you've been hurt, after that Canelo realised Khan couldn't hurt him so just cut the ring off more and more and walked through him like a machine, the fact Khan was turning into him trying to land a silly lead left just added to the force of the impact.
At the weigh in they looked of similar size but Canelo looked a different person during the fight and he's know to put mass back on really fast between the weigh in and the fight, 20 pounds Plus minimum.
Having said that back in the day fighters like Ray Robinson moved through the weights easily and never got banged out cold like that.
Makes you realise just how hard the old school fighters were