Newcomb came within one strike of throwing a no-hitter against the Dodgers at home on July 29.
Atlanta manager Brian Snitker had said Friday he would turn to Kevin Gausman in Game 3, but the Braves, who failed to score a run in losing the opening two games in L.A., instead will go with the 25-year-old Newcomb on Sunday in an attempt to extend their season.
Snitker said he discussed the change with general manager Alex Anthopoulos on the flight home after Atlanta's 3-0 loss Friday. They agreed on the move Saturday afternoon.
"We need to win," Snitker said Saturday. "Not that Gausman doesn't give us that opportunity; we like how Newcomb matches up with them and the success that he's had against the Dodgers this year."
Newcomb went 12-9 with a 3.90 ERA in 30 starts in his first full major league season, but he had a 5.68 ERA in 10 late-season starts. He threw 25 pitches in two innings in relief of Mike Foltynewicz in Thursday's 6-0 Game 1 loss, giving up a hit and a walk with two strikeouts.
Gausman, 27, is 5-3 with a 2.87 ERA in 10 starts since he was acquired from the Baltimore Orioles.
"Snit came up and talked to me on the plane before we took off, let me know that that was a possibility, so kind of get my mind right before I kind of went to bed," Newcomb said.
The Dodgers will counter with Walker Buehler, who pitched 6⅔ innings of one-hit ball in the NL West tiebreaker game against the Colorado Rockies on Monday. Buehler was 8-5 with a 2.62 ERA in the regular season.
Snitker said he might move switch-hitting second baseman Ozzie Albies up to No. 2 in the lineup, but he is not anticipating any changes to his starting eight.
"We've got to take the safety off and start firing," Snitker said.
Game 3 is set to start Sunday at 8:07 p.m. ET.
Information from The Associated Press was used in this report.