Ronald de Boer's late header proved enough to sink plucky Ayr's challenge as holders Rangers progressed into the fifth round of the Scottish Cup.

With championship rivals Celtic having enjoyed UEFA Cup success in midweek to set up the prospect of fixture congestion, Rangers were 11 minutes away from adding an unwanted replay to their own busy calendar.

But de Boer's intervention turned out to be the significant one and the Ibrox giants marched on.

Ayr had given them a scare however, not least when teenage substitute Stewart Kean fluffed an excellent equaliser chance following confusion in the Rangers defence.

In the first half there was only one moment when the First Division side had been prised open.

That was when Shota Arveladze latched on to a head-on from de Boer and, having lofted the ball over his marker, proceeded to smash the ball past goalkeeper Craig Nelson and on to the crossbar.

The Georgian put the ball into the net from his side's next attack but the flag was already up and Nelson was the equal of every other on-target effort until de Boer struck in the 79th minute.

Neil McCann and Barry Ferguson had fired early free-kicks over and if a defender was not in the way of a steady stream of long-range efforts then Nelson was.

Ayr made sure their defence was well-stocked at all times as Rangers played a waiting game that was calm, technically proficient but ultimately toothless.

Chances at the other end were few and far between. James Grady and Stephen Whalen buzzed about there was not a single shooting opportunity before he break.

Grady barged Lorenzo Amoruso over in the opening minutes and the defender needed treatment while the game continued.

He was soon back in action but Mikel Arteta limped soon after and did not return, having apparently hurt an ankle.

On went Stephen Hughes for a rare taste of first team action and he was unfortunate to see a header bounce wide after he was first to a rebound off the crossbar.

Hughes cut inside to fire just over after the restart and 10 minutes later Nelson pulled off an excellent save to deny Arveladze.

Kevin Muscat had come forward and he set up the Georgian, whose fierce, rising drive was palmed round a post by Nelson.

Ayr's first shot of the game arrived just before the hour mark but Scott Chaplain's long-ranger was straight at Stefan Klos.

Marc Smythe was in the way at the other end when Hughes drilled in a shot from a Numan lay back and the Dutchman was booked soon after for dissent after the award of a corner.

It almost proved significant as Ayr centre-back Mark Campbell was on the end of the corner only to head a good chance over.

Numan's response was to fire in a fierce drive that Nelson did well to block and, after Steven Thompson had gone on for Bob Malcolm, Hughes scuffed wide from close range before Arveladze headed a McCann corner over from six yards.

McCann was replaced by Claudio Caniggia at the same time as Ayr sent on Stewart Kean for Whalen and a chance came the youngster's way straight away.

The ball was loose after Grady and Numan had clashed just outside the box but the newcomer fired at the goalkeeper, as was the case at the other end when Arveladze tried yet again to beat Nelson.

But the long-awaited breakthrough arrived with 11 minutes to go and this time Nelson was powerless.

Thompson was the creator with some good wing play down the right, taking on his man and pumping in the perfect cross for de Boer to meet, and his header across Nelson gave the goalkeeper no chance.

Smythe and Grady were booked for fouls as the home side's frustration boiled over and Caniggia was inches away from making it 2-0 with a shot that went inches wide.

But the tie was still in the balance and, after Moore was booked for retribution on Grady, a breakdown in communications at the back almost cost Rangers an equaliser.

Amoruso left a high ball for Klos but Kean was there first. The youngster was soon holding his head in his hands though after failing to loft the ball over the goalkeeper and into the empty net.

Grady fired another good chance over as Rangers held on unconvincingly to make sure their name was in the draw for the next round.

Teams

Ayr Nelson, Campbell, McManus, Craig, Lyle, Smyth, Chaplain, Murray, Lovering, Grady, Whalen (Kean 73).

Subs Not Used: Dunlop, Nicolson, Latta, Dodds.

Booked: Smyth, Grady.

Rangers Klos, Muscat, Moore, Amoruso, Numan, Arteta (Hughes 21), Malcolm (Thompson 62), Ferguson, McCann (Caniggia 73), de Boer, Arveladze.

Subs Not Used: McGregor, Bonnissel.

Booked: Numan.

Goals: de Boer 79.

Att: 9,608

Ref: Alan Freeland (Scotland).