Rangers re-established their four-point lead over Celtic in the SPL with a win over Kilmarnock at Rugby Park.
Cuellar was on target for the league-leaders
Defender Carlos Cuellar headed the first after 24 minutes as Kilmarnock failed to clear a Kirk Broadfoot cross.
Sasa Papac preserved the away side's lead by heading Allan Johnston's goal-bound drive over the bar as Kilmarnock pressed for an equaliser.
But the points were sealed on 63 minutes when Kris Boyd smashed in a penalty after Jamie Hamill's handball.
The Ibrox side were looking to restore their four-point lead in the league, while Kilmarnock were in desperate need of points to take them away from the foot of the table.
Shorty after kick-off it was Walter Smith's men that looked the more likely to succeed in their task, and they should have taken the lead within two minutes.
Boyd headed on a high ball for Jean-Claude Darcheville, who collected and raced between Killie's central defenders.
But the Frenchman lifted the ball over both the on-rushing Alan Combe and the Kilmarnock crossbar.
Kilmarnock showed they were not content to contain the table-toppers, and came close through Craig Bryson on 11 minutes.
The midfielder skipped past Brahim Hemdani and curled a low shot from 22 yards that sneaked just past Allan McGregor's left-hand post.
Rangers winger Chris Burke was seeing lots of the ball on the right side of midfield.
And Darcheville was inches away from taking the lead midway through the half, but was unable to get his boot to a Burke corner that dropped at the far post.
But the Ibrox side broke the deadlock moments later.
Kirk Broadfoot delivered into the box, and the ball eventually fell to Cuellar, who coolly headed back across goal and inside Combe's post.
Kilmarnock nearly pulled back a quick equaliser from a Simon Ford looping header that McGregor was glad to see land on the roof of the net.
The home side continued to press, although a number of their attacks were thwarted by offside calls.
But Darcheville passed up an excellent chance to double Rangers' lead minutes before the break.
The striker again used his blistering pace to beat the Killie defence to a long ball.
But with only the keeper to beat, he lacked composure and screwed his shot wildly past the post as Rangers took a slender lead into the half-time break.
However, the Ibrox side were eager to secure the points, and Combe was called on within minutes of the re-start to tip a powerful Boyd free-kick round the post.
The home side were continuing to battle and Johnston's thunderous strike from 18 yards was diverted over off the head of Papac on the hour mark.
But just as Kilmarnock were gaining a foothold in the match Hamill handled in the box and Boyd made no mistake from the spot as he became Rangers' all-time record SPL scorer.
Kilmarnock manager Jim Jefferies' decision to bring on David Fernandez almost paid dividends six minutes from time.
The Spaniard intercepted a poor pass-back from Broadfoot, but after rounding McGregor he could only steer his shot wide from a tight angle.
And at the other end Combe was alert to prevent a third as he saved Lee McCulloch's flick from close range.
Kilmarnock: Combe, Fowler, Hay, Frazer Wright, Ford, Locke (Di Giacomo 87), Johnston (Fernandez 71), Hamill, Bryson, Taouil (Gibson 79), Invincibile.
Subs Not Used: Harpur, O'Leary, Clancy, Corrigan.
Booked: Locke, Hamill.
Rangers: McGregor, Broadfoot, Papac, Cuellar, Weir, Ferguson, Hemdani, McCulloch, Burke (Novo 75), Darcheville (Naismith 75), Boyd.
Subs Not Used: Alexander, Davis, Dailly, Furman, Fleck.
Goals: Cuellar 24, Boyd 63 pen.
Ref: M McCurry.