Shields will be pushed back to Game 6, if needed, Maddon said, because he wants Shields to pitch at home, where he is "very good."
The Rays lead the Boston Red Sox 3-1 in the ALCS and can close out the series with a win in Game 5 on Thursday at Fenway Park.
Kazmir (0-0) has struggled so far in the playoffs, posting a 6.52 ERA in 9 2/3 postseason innings. He went 4 1/3 innings in Game 2 of the ALCS, allowing five earned runs and taking a no-decision in the Rays' marathon win.
He'll go against Daisuke Matsuzaka (1-0), who has allowed only three runs in 12 innings this postseason.
"We're not looking to give them any kind of crack" in the door, Maddon said Wednesday, a day after his team beat Boston 13-4 to take command of the best-of-seven series. "We believe that Kaz can pitch well tomorrow. We're just trying to look at the big picture with the whole thing."
Maddon said this was part of the plan all along, helped in part because of the travel day Friday that would allow the bullpen to recuperate if Kazmir can't go deep into the game. Kazmir's numbers at Fenway Park are also better: He is 4-4 with a 3.02 ERA at Fenway; he has a 2-3 record and 4.29 ERA against the Red Sox at home.
Shields is 1-1 in the playoffs, beating the Chicago White Sox in the ALDS. He took the loss in Game 1 of the ALCS, despite allowing only two runs on six hits in 7 1/3 innings. He has a 3.29 ERA in 13 2/3 innings this postseason.
On the other hand, Shields is 0-3 in three starts with a 10.13 ERA at Fenway.
"This has not been his most effective place to pitch, and he's been very effective at home," Maddon said. "Kaz has been good here. And again, you look at what Kaz has done recently, and I understand everybody's trepidation, but I feel strongly about it, we all do. We feel it's the right thing to do right now."
The defending World Series champions have lost three in a row to fall to the brink of elimination, but it's a position that has served them well: They're 7-1 in elimination games since 2004, including a Game 7 victory in last year's ALCS over Cleveland -- a game won by Matsuzaka.
"Believe me when I tell you, how he pitches this -- the intensity, the meaning, as much as this game means, that will help him," Red Sox manager Terry Francona said. "That won't hinder him."
The Red Sox have twice come back from a 3-1 deficit in the ALCS -- in 2004 they trailed the Yankees 3-0 -- to reach the World Series.
"If we can draw on anything from that, good," Francona said. "Anything that's happened in your past -- you try to turn it into an advantage for you. Saying that, this is a different team, it's a different Tampa team. But, again, we'll use anything we can to give us any kind of advantage."
The Rays' move also allows Kazmir to avoid any run-ins with veteran umpire Derryl Cousins, who is scheduled to work behind the plate in Game 6. Kazmir had angry words for Cousins following a June 11 game against the Angels, accusing the umpire of missing strike calls during key at-bats and making makeup calls. Maddon was ejected for arguing balls and strikes with Cousins during that game.
"That was unbelievable. I've never seen anything like that before," Kazmir said after that game. "I mean, you come into the game and some of the veteran guys are talking about an umpire that doesn't like calling anybody out on strikes. They called him 'shoe box.' You shouldn't change your zone just because of the count."
Cousins, informed that Kazmir had called his performance "unbelievable," "ridiculous" and "amazing," had his own words for the left-hander, according to the St. Petersburg Times.
"I didn't know he's been around that long," Cousins, a 28-year veteran, said after that game, according to the Times. "I've got nothing to say. It won't be the first time or the last time that he says something."
Information from The Associated Press was used in this report.