Urias is not injured, which means Knebel will probably serve as an opener, paving the way for Urias to handle the bulk of the innings beginning with the bottom of the second from Oracle Park in San Francisco on Thursday night.
"Why we did it, I think it's more appreciating in one game what gives us the best chance to win,'' Dodgers manager Dave Roberts said.
Roberts said Urias was "all in'' on going this route when they spoke, noting the lefty likely will still pitch for a key stretch.
The San Francisco Giants stacked their right-handed hitters at the top of their lineup against Urias in Game 2. Knebel starting against them would take away the Giants' platoon advantage in the first inning, potentially shortening the game even further.
Giants manager Gabe Kapler said he received a courtesy text message from Roberts on Wednesday night to let him know about the switch.
"We have that good quality relationship that we'll communicate on things like that," Kapler said.
Urias will be on four days' rest and can take on a traditional starter's workload, but given the stakes, he'll probably be removed at the first hint of trouble.
Roberts said Wednesday that Max Scherzer, who threw 110 pitches in a Game 3 start on Monday, is "highly unlikely" to be available out of the bullpen.
The Giants will start Logan Webb, who threw 7 scoreless innings in Game 1, but Kevin Gausman will be fully rested behind him. Knebel opened four games for the Dodgers this season, allowing one run in a total of five innings.
The Dodgers famously used Dustin May as an opener in Game 7 of the 2020 NL Championship Series, an eventual victory that saw Urias finish the game with three scoreless innings.
--The Associated Press contributed to this report.