That was the first time since his sophomore year at Alabama that Richardson wasn't his team's starting running back.
Richardson, the No. 3 overall pick in the 2012 draft, isn't blaming others for his demotion.
Not coach Chuck Pagano. Not the offensive line. Not quarterback Andrew Luck. Not offensive coordinator Pep Hamilton.
Richardson blames only himself.
"It was different when I went out there Sunday," he said. "It was kind of like this is a place in your life where you have to learn and really see the offense and how things flow. I learned about myself Sunday, how humbling it was. I have to step up. I have to make sure I'm doing my job."
Richardson talked with confidence Thursday, saying in his first extensive interview other than giving a brief comment to ESPN.com after Sunday's game that he knows he'll bounce back.
The Colts acquired Richardson on Sept. 18, and he was playing three days later at San Francisco and in the starting lineup Sept. 28 at Jacksonville.
That shouldn't have been the case now that Richardson thinks back on it.
"I think it's only fair that Donald is the starter, especially the production he's been putting up and the numbers," Richardson said. "He's been playing good ball. I tell people all the time that when I first got here, they thought it was a two-headed monster with me and Ahmad [Bradshaw]. I always said it was a three-headed monster."
Richardson has only 306 yards on 108 carries this season while not looking like the running back who starred at Alabama and rushed for 950 yards as a rookie with the Browns last season. He hasn't rushed for more than 60 yards in a game this season.
He was in a tough position, having to learn the Colts' system on the fly, and he said that's affecting him because he's thinking too much instead of relying on his instincts on the field.
"It slows you down," Richardson said. "Trust me, it's a lot different. When you're thinking about it, it really slows you down.
"I talked to my granddaddy and uncle, and they said, 'No matter what, you're still Trent Richardson. You're hard on yourself because you expect a lot out of yourself. That's how you've always been.'"
The Colts are fully invested in Richardson and have no intention of cutting him loose in the offseason, a source told ESPN.com.
He's only 23 and still has a future with the franchise. Indianapolis will continue to use a running back by committee approach with Richardson and Brown.
"It's going to happen," Richardson said about playing better. "Over these last two weeks I was able to sit down and dig my head into it. Right now I feel good."