Smith felt a second-half strike from Kris Boyd which was disallowed for offside should have been allowed to stand.

Instead, the match at Fir Park ended goalless as Rangers slipped four points behind Celtic, who ran out 3-0 winners at Kilmarnock.

Murphy was also involved when Scott McDonald netted in April's Old Firm derby at Celtic Park, which the home side won 3-2, and Smith insists he got it wrong again.

"We didn't finish well and the one that we did finish through Kris Boyd was a poor decision from the linesman," Smith said.

"I think it was quite clear it was onside. Mr Murphy was quick to allow a Scott McDonald goal at Celtic Park and was quick to disallow that [Boyd goal].

"That's two away from home this season, at Aberdeen and here again tonight, that the linesmen have got wrong.

"But, over and above that, we have our own side to look at and we did create enough opportunities to win the game."

The only plus point for Rangers was skipper Barry Ferguson making his first start of the season and coming through the full 90 minutes.

Smith added: "It was a good game for him to come back because, although it was 0-0, it wasn't a dull 0-0.

"I had no intention of keeping him on for the 90 minutes but, as it went on, he said he was okay. He has a good base of fitness anyway and I'm pleased he has that type of 90 minutes under his belt."

Motherwell boss Mark McGhee felt his side should have had a penalty when John Sutton claimed to have had his jersey tugged late on.

But McGhee had no real complaints about the outcome, adding: "Defensively it's the best forward line we'll play against for a long time and it's the best clean sheet we will get for a long time so I was well pleased.

"I can't say we deserved to win the game but it was a good game and I'm pleased with the way we played."

The Motherwell boss also paid tribute to goalkeeper Graeme Smith, who became a father when his girlfriend Cheryl gave birth to a baby girl named Mia last night.

McGhee, a new father himself, said: "He became a father last night and I think he has taken inspiration from that.

"He has played very well but I can hardly single him out because everyone played well.

"There was only a chance of him not playing if it had gone on until tonight but because the baby was born yesterday that wasn't the case.

"He has been playing well, I think he is much improved. When we got here he could hardly clear the halfway line but he has been in the gym and has improved enormously in his strength.

"His confidence is up because of his physical fitness and strength. He played very well tonight. He is a father now and with that comes a lot of responsibility and that will only do him good."