The Engineer's started building a little further back from the tunnel after he'd been killed the last time. Directly across from the first checkpoint is a little alcove, protecting the sentry, teleporter, and dispenser from death from above. Unfortunately, the close quarters makes it perfect for a Pyro to flame everything to death.

"Dagnabbit!" the RED Engy exclaims as the ubered duo come around the corner. He's already falling back, knowing a lost cause when he sees it.

The poor sentry's only level 2. It doesn't even have rockets to push them back with, yet.