I had less of a problem with him coming in in the 7th, and even pitching the 8th. It was an elimination game, with the heart of the order coming up.
But with a 9-2 lead in the 9th, it was foolish to have him start the inning. It was only 5 pitches, but add in his 8 warmup pitches, even if they were only at 80-90%, that's an additional 13 pitches that didn't need to be thrown by him with a seven run lead.
I was surprised that neither Smoltz nor Buck commented that Chapman's fastball was "only" clocking in at 98/99 while facing Guyer in the 9th (I think one pitch hit 100), rather than the 100/101/102 he'd been routinely throwing to everybody else on Sunday, and in the 7th/8th last night.