Centre-back Cuellar headed Rangers in front in the first half, and former Kilmarnock striker Kris Boyd doubled their lead with a penalty after the break.

Smith believes Cuellar, whose goal was his fifth of the season, is playing a key role for Rangers.

"He is a threat. He's playing very well for us a the present moment," Smith told Setanta 1.

"I felt he played very well today, as he has done steadily over the season.

"He's chipped in with his goals which are important ones and that was an important one today."

Smith confirmed Rangers were "delighted" with victory against a spirited Kilmarnock side, which reasserted his side's position above Celtic at the top of the SPL.

He is now hoping his side can achieve another away victory when they face Panathinaikos in Greece on Thursday, in the second leg of their UEFA Cup tie.

The first leg at Ibrox was goalless, and Smith anticipates a tricky return fixture, but the Rangers boss insists his side can reach the last 16.

"It will be a difficult game," he said.

"We're confident enough in terms of our overall defending, so we can try to go to score goals away from home, as we have done this season at Stuttgart and at Lyon, and hopefully we can get them in Athens on Thursday."

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Kilmarnock manager Jim Jefferies was pleased with the effort of his second-bottom side who had plenty of the play.

"I was delighted with the performance," Jefferies told Setanta 1.

"We played an attacking game and people were up on the ball today; in fact we were on top in the second half until the penalty. It came against the run of play.

"There's a lot of encouraging signs for the games ahead."

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Rangers frontman Boyd was left on the bench for the first match against Panathinaikos but started against Kilmarnock and hopes he can regain his role as a regular in Smith's side.

The striker has frequently been a substitute this season, despite his outstanding goals-per-game record.

"It's obviously frustrating," Boyd told Setanta 1, "but you get your head down and work hard in training and hopefully over the next few weeks I can establish myself back in the team."

He is eager to play a full role in the rest of the season as Rangers attempt to end Celtic's two-year reign as Scottish champions.

Boyd said: "We wanted the title back and we're on the way to doing that.

"But there's a long way to go yet, and I'm sure Celtic will make it hard the way they're playing just now.

"Hopefully we can match them and we can win the league."