Ken Macha did what any player's manager would do. He went out to the mound and asked Barry Zito if he still wanted to stay in the game after 120+ pitches. Zito insisted he was fine and wanted to stay in.
I think this was a result of last season's game 161 against the Angels when Zito had said that he was done and pulled himself from a game. He received a deluge of criticism at the time. People said over and over, Zito needs to grow a pair. Well, tonight you saw the residual effect of that game in Zito's psyche. He demanded to stay in the game. Granted, Macha could've overruled him, but that's also how you sometimes lose a player. Zito emphatically asked to stay in. He threw a good pitch to Belliard. It wasn't a hanger.
If you've noticed throughout the season that Zito has been left in games whereas someone like Saarloos would've had a quick hook. And Zito has earned that as the veteran of the staff. The analytical side says, take him out there, but you engender the trust of a player when you give them the opportunity to succeed there. Belliard just hit a good pitch for a home run. And honestly, the bullpen hasn't been that much better of late.
I still think that game (and the ensuing public criticism) against Anaheim made Zito into what he is today, which is a player who wants to overextend himself to prove his toughness.
Macha could've pulled Zito and he probably should've, but he trusted his player. You can call it a mistake all you want. I don't think Zito feels that way which is probably all that matters to Macha.