I am going to need to rewatch the game but at the time I felt that the problems we were having in the first half were mainly (not exclusively) because Alderwierled was man marking Sancho, I don't recall us ever doing this, I may be wrong with that but genuinely can't recall our back 4 or 3 man marking a player, we tend to be well drilled line, defend spaces not the individual (we've man marked in other areas in midfield eg Dele on Jorginho). Anyway, I felt because of this Toby was pulled out of defence on numerous occasions, which created holes which weren't filled/covered by Winks/Sissoko/whoever.
Yes, Vertonghen wrapped up Sancho in 2nd half as a result of attacking them, which meant Sancho (and his teammates) were more concerned with defending than attacking us.