"Carlos can do that job if his mind is totally set on it," Piniella said. "He helps us in so many areas by being out there, because he frees me to use other pitchers a lot different than if he wasn't out there.
"His presence alone is a big help."
Zambrano gave up three runs on four hits in his one inning of work on Friday. He came in with a tie and left with a loss. His ERA ballooned to 7.07. He has allowed six runs over 8 2/3 innings in eight relief appearances.
"Listen, I was unhappy the first day they told me that," said Zambrano of going to the bullpen. "I wasn't sure it was going to work. But now, I accept it. I'm a reliever now and I have to do my job as a reliever, as a set-up man. I'm happy now."
Piniella had to remove Zambrano in the eighth inning on Wednesday after he had given up two hits and had two outs. The Cubs went on to beat the Florida Marlins 4-3.
"I wanted him to finish the eighth inning, but I brought [Carlos Marmol in with two outs and we held on and won a baseball game."
Piniella was asked if Zambrano has bought into the set-up man role.
"When he goes out there, he gives you everything he has," Piniella said Friday afternoon after hesitating. "He really gives you exactly what he can give you.
"When he steps on the mound, I have no doubt his full intention is to get everybody out and be as dominant as he can. Now, do we keep that train of thought prior to the game? In preparation, that sort of thing? It's a different mindset, and I understand that wholeheartedly. Once again, I've said this many, many times, I'm very appreciative of Carlos going to the bullpen."
Zambrano was moved to the bullpen on April 22. He was 1-2 with a 7.45 ERA as a starter.
Information from The Associated Press was used in this report.