Mark Prior

I'm watching the Cubs-Mets game, and the Cubs just gave up a run in the 9th to make it 3-2 in their favor. Mark Prior is still on the mound. I have to ask: There is a consensus in baseball that Prior is wearing down. He is a young pitcher who has never thrown this many innings before. So why is he still in the game and not Borowski? Is the bullpen really that atrocious? I understand Prior missed a month, but still wearing down is wearing down. All well...I've been distracted with other things, so maybe his pitch count isn't that high.