Lewis, who allowed four earned runs over five innings while throwing 109 pitches in a loss against the Astros on Friday, was scheduled to start Wednesday at Angel Stadium but will now start the series opener in Chicago on Friday.
"We just want to give Colby as many days as possible," Rangers manager Ron Washington said.
Lewis has been a big part of the Rangers' success this season, with a 7-5 record and 3.28 ERA in his first year back in the Majors since 2007 after spending two years playing in Japan.
"Colby has been big for us and we want to keep him strong the whole year," Washington said. "Giving him a little extra rest now should pay off down the road."
Beltre, meanwhile, will get his first Major League start on Wednesday in place of Lewis after posting an 0-5 record and a 2.39 ERA in 15 appearances, five starts, with Triple-A Oklahoma City. The 28-year-old also struck out 44 batters in 37 1/3 innings.
"Beltre has been throwing well for Oklahoma City, and we wanted to give him an opportunity when he's going good," Washington said.
Beltre is scheduled to be added to the 25-man roster before his start on Wednesday and a corresponding roster move will be made prior to that game. Prior to this year, Beltre had not pitched in the United States since 2004 because of visa issues, which did not allow him to enter the U.S. from 2005-09.
He was on the 40-man roster restricted list from April 1, 2006, until being reinstated on Feb. 19, 2010, upon arrival at Spring Training in Arizona. He was originally signed by Texas on March 1, 2000.
The rest of the scheduled rotation is as follows: right-hander Scott Feldman will start Tuesday and left-hander C.J. Wilson will start Thursday against the Angels. Right-hander Tommy Hunter starts Saturday and Feldman starts the series finale on Sunday against the White Sox.
Rhett Bollinger is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.