Scott Sinclair scores twice from close range for Celtic after being denied from the spot
Timothy Weah marks debut with goal to make it three for holders
10-man St Mirren come from two goals down to beat Alloa
Mark McGuigan's header earns Stenhousemuir a draw at Aberdeen
Ross County hold on as Brian Graham's double edges out Motherwell
McCracken header gives Junior side Auchinleck famous win
Auchinleck Talbot v Ayr United (12:15)
Beechwood has a reduced capacity of 3,100 for this sold-out encounter, with 1,700 tickets going to home supporters. The population of Auchinleck is just 3500.
Auchinleck Talbot v Ayr Utd (12:15)
Jane Lewis
BBC Sport Scotland at Beechwood Park
Quote MessageBeechwood is bursting at the seams. A typically tight ground and already the atmosphere is terrific. Both sets of fans in full voice. This should be a cracker of a cup tie.
Auchinlek Talbot v Ayr United (12:15)
Auchinleck Talbot: Leishman, Lyle, McPherson, McCracken, Pope, White, Wilson, Armstrong, Hyslop, Glasgow, Wilson.
Substitutes: Samson, Kemp, McIlroy, Shankland, Waite, Hewitt.
Ayr United: Doohan, Geggan, Rose, Higgins, Harvie, McDaid, Murdoch, Docherty, Crawford, Moffat, Moore.
Substitutes: Hare-Reid, Smith, Hilton, McGuffie, Ferguson, Bell, McCowan.
Referee: Euan Anderson
Auchinleck Talbot v Ayr United (12:15)
Ayr United are only three points behind Championship leaders Ross County but Ian McCall's side have been wobbling a bit of late and are without a win in five games, losing their last two league outings.
Top scorer Lawrence Shankland missed those two defeats with a calf injury and the prolific striker is once again missing today.
There is a Mark Shankland on the home bench, no relation...
Image source, SNSLawrence Shankland has scored 28 goals in 26 appearances this season
Auchinleck Talbot v Ayr United (12:15)
Biffy Clyro frontman Simon Neil welcomes the Scottish Cup to Ayrshire.
Auchinleck Talbot v Ayr United (12:15)
Today's action starts with an Ayrshire derby, with Championship promotion contenders Ayr United visiting Auchinleck Talbot.
The hosts play in the junior ranks but they are no strangers to the Scottish Cup and the club is steeped in silverware success at their own level.
The TV cameras are at Beechwood Park, with Sportscene starting on BBC One Scotland at noon.
The winter break is over and, as luck would have it, the first scheduled match for a Premiership side was postponed due to the plummeting temperatures.
Rangers' Friday night visit to Cowdenbeath was called off, with a section of the Central Park pitch frozen, much to the annoyance of the League Two club, who had enlisted the help of fans to lay down covers.
"If it was Berwick Rangers, the game would have gone ahead in my opinion," said disappointed manager Gary Bollan.
There's no suggestion of any call-offs today.
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Who will get their hands on the oldest trophy in world football this season?
The Scottish Cup has reached round four and that means all of the big boys are getting involved this weekend.
Holders Celtic are going for three in a row for the first time in their history but will Brendan Rodgers' side reach the final on 25 May?
Here's a refresher on the ties we have in store (all kick-offs 15:00 unless stated).
Aberdeen v Stenhousemuir
Auchinleck Talbot v Ayr United (12:15)
Celtic v Airdrieonians (17:15)
Cowdenbeath P-P Rangers
Dundee v Queen of the South
East Fife v Greenock Morton
Inverness Caledonian Thistle v East Kilbride
Heart of Midlothian v Livingston (Sun)
Hibernian v Elgin City
Kilmarnock v Forfar Athletic
Montrose v Dundee United
Motherwell v Ross County
Partick Thistle v Stranraer
Raith Rovers v Dunfermline Athletic
St Johnstone v Hamilton Academical
St Mirren v Alloa Athletic
Image source, SNS