I still wouldn't put the ace label on him, both because of the innings thing and his reliance on his defense. But the longer he keep this HR and general hit suppression up, the more inclined I am to think that this is "real". That said, we shouldn't ignore that Johnny's peripherals have improved this year. His strikeouts are up and his walk rate is down by 1/3, dropping his FIP by 40 points to just above 3.00. His BABIP is back to normal, but he's still suppressing HR and now is benefitting from some nice LOB "luck" -- though there's obviously some overlap there.
I still don't think an ERA south of 2.50 is sustainable, but I'd be quite happy with one in the high 2s or lower 3s. Though he has been one of the most effective SP in the game over the last year (lowest ERA in baseball over the last 2 years I believe), I'd still label him a soft 1, very good 2. If Mat Latos can build on what we saw last night, I'd feel pretty good about the top of the rotation - though I'd still like to see Chapman be given every opportunity to be ready to be our Game 3 SP come October.