Scottish Cup: Airdrieonians v Hearts
Venue: Excelsior Stadium, Airdrie Date: Sunday, 11 February Kick-off: 17:00 GMT
Coverage: Watch on BBC One Scotland & iPlayer, listen on BBC Radio Scotland Extra/DAB/810MW, follow live text coverage on the BBC Sport website & app
There's already been one surprise in the Scottish Cup and 14 teams have their sights set on the seven remaining quarter-final places.
Morton's Friday night win over Motherwell may have set the tone for shocks, with the second-tier team triumphing 2-1 against their Premiership visitors.
The big two from Glasgow will be expected to go all the way unless they are drawn against each other - but there is plenty of hope for those outside the country's superpowers, with three non-Old Firm finals over the past decade.
Let's take a look at what's coming up.
Thistles threaten to sting
There are three more Championship sides at home to top-flight opposition, including Airdrieonians v Heart of Midlothian on Sunday, which will be broadcast live on the BBC. The Diamonds are unbeaten in seven, only conceding twice during that run.
Elsewhere, Inverness Caledonian Thistle and Partick Thistle will fancy their chances against Hibernian and Livingston respectively, but that's possibly more to do with the terrible form of the visitors.
Partick destroyed Ross County in the previous round, making up for some of the pain of last term's dramatic play-off defeat.
Livingston's only victory since early October came on the same afternoon as they edged out Raith Rovers in West Lothian and David Martindale's strugglers may feel even more deflated after losing out to a late goal at Rugby Park on Wednesday.
Although there was a marked improvement in the cruel midweek loss to Celtic, Hibs have looked a soft touch under Nick Montgomery too often and their only win from their past eight outings was a rather fortunate 1-0 away to Forfar.
However, last season's surprise runners-up have struggled at Caledonian Stadium of late, taking just one point from their past five home league games and failing to score in the past three.
Getting to know you
Next we come to two ties involving sides that have not met before, which is rare at this stage of the tournament.
Neil Warnock has never taken a team to a cup final and it would be a major shock if Aberdeen don't get their temporary boss a step closer at home to League Two Bonnyrigg Rose, the lowest-ranked side still standing.
Sean Connery's old team have won the Junior Cup twice but this is the furthest they have been in this competition.
Kilmarnock also start as big favourites against Cove Rangers given the gulf in divisions and their impressive home form.
There was an Old Firm double in August and Killie have lost just two of their past 13 on their own plastic patch - both to Hearts - while the arrivals of Greg Stewart and Kevin van Veen have strengthened a streetwise squad.
Cove have gone off the boil without a League One win in five attempts since the turn of the year and needed extra time to get past Highland League Brora Rangers.
What about the Old Firm?
Rangers will be expected to rack up a 20th victory under Philippe Clement without too much fuss. The Belgian has hauled his side right back into the title race with just one defeat in his 23 games since replacing Michael Beale.
Todd Cantwell is enjoying a purple patch, with five goals in his last eight appearances, the oft-maligned Cyriel Dessers has quietly crept into double figures, John Lundstram has been re-energised and Ridvan Yilmaz is finally looking the part.
Ayr United are huge underdogs but new manager Scott Brown knows a thing or two about winding up the Ibrox crowd. The presence of the former Celtic captain is sure to make for a more heated atmosphere than usual for these kind of David v Goliath fixtures.
Ally MacLeod was in charge of the Honest Men when they last beat Rangers, in October 1975, and you have to go all the way back to 1959 for an Ayr United victory at Ibrox.
Finally, we get to cup holders Celtic, who look a little out of sorts and have a tricky assignment in Paisley.
St Mirren took four points off the champions last season but took three hidings in between and have lost both league meetings this time round, suffering an early blitz at home in the last weekend before the winter break.
Celtic have been unconvincing since the campaign resumed without it being too costly. There have been uncharacteristic struggles in front of goal as chances galore were squandered in the win over Ross County and the draw at Aberdeen, while they created little against Hibs, relying on two penalties to get them over the line.
Their wingers have been subdued and supporters will have been puzzled to see top scorer Kyogo Furuhashi on the bench at Easter Road. The bright note was a confident spot-kick double from new arrival Adam Idah coming after his team's four penalty misses this term.
St Mirren will have noted Hibs and the Dons gave Celtic a fright when taking the shackles off, but that's easier said than done against the heavyweights.