And I would add that a game like that is a perfect time to get a guy like Lopez work in a low leverage situation to work out some kinks. It obviously went poorly, but that's why you do it. You have some room for error.
Plus, there's still a lot of season left and the young starters are already being relied on heavily. And as @IndianaTwin noted, they're coming up on a stretch of 28 games in 30 days. Fresh bullpen arms are easier to cycle through than the rotation guys.
I wouldn't have been upset if Varland came out for the 8th, but I don't think it was necessary and there were better uses for that situation in my opinion.