That was my thought (except if Smith gets the first 2 in the 8th, I would have left him in to finish the inning).
But,
Sometime last season, one of the national color commentators (a pitcher, so either Kaat or Hersheiser) opined that the reason many relievers (especially closers) don't fare well in multi-inning situations is that they are not used to throwing an inning (or part of one), sitting down for 10 or 15 minutes and then going back out there. A starter does that all the time, relievers don't. The reasoning makes sense. Kelly has been fairly successful at it, but he isn't that far removed from his starting days. Johnson did a good job last night. Ditto. The guys who suck at it have been relievers for years.
Starters will throw simulated games in the pen. Maybe relievers should throw simulated multi-inning stints in the pen (2-3 innings), especially in spring training.