"[Brown] earned the opportunity the way he was working and running the football," Colts coach Chuck Pagano said. "We're still going to use two backs, but [Brown] earned the opportunity to get in there and do that."
The Colts prevailed 22-14 in the key AFC South matchup. Brown rushed for 54 yards on 14 carries and scored a fourth-quarter touchdown that put Indianapolis ahead by the eventual winning margin. Richardson received five carries in the game and gained 19 yards.
"As a competitor, you want to play, but at the end of the day, you can only control the things you can control," Richardson told ESPN.com. "Donald's production has been better than mine.
"It's all about the team and the coaches put the team in the best position to win. Coach made the call. Whatever it is, you have to be happy with it because obviously we're winning."
But Richardson, the No. 3 pick in the 2012 draft, has struggled, averaging 2.9 yards a carry and having yet to rush for more than 60 yards in a game this season entering Sunday's games.
Pagano informed Richardson of his decision earlier this past week.
"[Richardson] handled it awesome," Pagano said. "[He} came to work, put his time in, prepared and was ready to go."
The Colts made the move trying to jump start an offense that had been outscored 93-12 in the first half of the four games before Sunday.
Brown opened the season as the third-string running back but he's been the team's most consistent back this season. He had 80 yards and two touchdowns against the Titans on Nov. 14.