It's a bit like that old saying in football - you're most vulnerable after you've just scored. It's the same for most sports I guess, when you make a breakthrough (especially after trying for ages to do so) it's natural for concentration levels to drop.
And I've seen Andy breaking back right back half the times if not more. Very good strategy.
Wonder though if Zeballos will get a win here. May go all mental at the right time. That will be his biggest testament in this match. He looks to me as the better player right now.