I just had another look at Sergio's on board. He touched the back left of Carloz who was slowly drifting towards him. Could have been avoided by Sergio.
It's kind of irresponsible to be racing at that time of day if drivers end up going down a straight blind like that. They should probably move the start to a bit earlier in the day.
Russell said he couldn't see shit going past the accident and they were lucky they both were on the side of the road and hadn't bounced back into the middle.
My guess is that both were trying to catch Leclerc's slipstream and were focused on Leclerc and not each other. That said if I had to assign blame I think it's more on Perez than Sainz.
I thought he was drifting slightly right to go towards the racing line. Sainz was drifting more though. Still I think perez was much better placed to prevent that crash