Motherwell boss Stuart McCall says his side failed to capitalise on Rangers' injury troubles as they lost 3-0 at Fir Park.
Injury and registrations problems meant youngsters Jordan McMillan and Ross Perry started in defence for Ally McCoist's side.
"I thought we should have done better against their inexperienced defenders," McCall told BBC Radio Scotland.
"But they still had the players to hurt us, and they did that."
Rangers went ahead through a Steven Naismith goal after 20 minutes, before strikes from Kyle Lafferty and Gregg Wylde ended Motherwell's run of clean sheets.
"If you are going to beat the Old Firm you've got to score first," McCall added.
"The goal just before half-time killed us.
"Then the second and third goals came on the counter attack.
"I'm really disappointed because I thought we could have done better today."
But the former Rangers player says he does not think his side can be measured by their results against the Old Firm.
"We're not going to be judged by what we do against Rangers or Celtic," he said.
"We'll be judged by what we do against the rest of the sides: Dundee United, Hibs and Aberdeen.
"As nice as it would have been to get a result today, it just wasn't for us."