Walter Smith was upset with his side's defending at both Celtic goals
Rangers manager Walter Smith believes his side paid dearly for defensive mistakes in the 2-0 defeat by Celtic.
Georgios Samaras fired a double - one from the penalty spot - to secure victory for the visitors at Ibrox.
"Giving away the goals we did today maybe isn't like us," Smith told BBC Scotland afterwards.
"Celtic defended very well throughout the match and we were unable to create the opportunities we'd have hoped. We contributed to our own downfall."
The defeat leaves Rangers four points behind league leaders Celtic, but the defending Scottish Premier League champions have two games in hand.
"I felt we started the game well and played very well in the first half-hour and probably were the better side in the first half," said Smith.
"Celtic, in fairness, started the second half better than we did. Once the game settled down again, I thought it would be down to which team managed to score the first goal.
"We're unhappy with the manner in which we lost both the goals."
Smith admitted that his Rangers side lacked a cutting edge in the final third, adding: "Neither goalkeeper had a great deal to do during the game.
"That was one of the annoying factors for us at half-time. We had the majority of the ball but didn't create a great deal.
"We only have ourselves to blame for that."
The Rangers boss, who will be stepping down at the end of the season, reiterated his desire to see some signings to bolster the Ibrox squad.
The league championship could turn out to be one of the most exciting we've had for a number of years
Rangers manager Walter Smith
"We're threadbare and have been like that since the start of the season," said Smith.
"In today's game, we contributed to our own downfall. Celtic defended very well throughout the match and we were unable to create the opportunities we'd have hoped.
"You only have to look at the two goals to see we have to shoulder responsibility for both of them.
"That's got nothing to do with the size of our squad or anything like that."
Rangers trail Celtic by four points but have two games in hand and Smith believes the title race will go down to the wire this season.
"You read ridiculous things like if Celtic had lost this game then they were out of the championship race," he said.
"People make too many assumptions and I don't think we're even at the halfway stage of the championship yet.
"There's a lot of football still to be played; Hearts are doing extremely well, so the league championship could turn out to be one of the most exciting we've had for a number of years."
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