I don't even think he messed up. For the first goal Aguero was brilliant and I would put more blame on Becker for failing to cover his near post.
For the 2nd goal it was a superb run by Sterling, a brilliant finish by Sane and I don't think Lovren should be getting flak for that.
Saving a ball travelling at the speed Aguero hit it would be pure luck. I would imagine it would have been travelling at something like 50mph perhaps even more. If he picked the right spot which he clearly did no goalie on Earth would have stopped that.
I’m sometimes amazed by how supporters generally laud a player for scoring an unstoppable shot from 30 metres but berate a goalkeeper for failing to stop a shot travelling at the same speed from a few metres. If the player finds a gap big enough to squeeze the ball through and its on target that’s it ...... nothing the goalie can do.