Leeds have struggled at this stage of the competition in recent years, getting knocked out in the third round three times in a row.

Meanwhile, Crawley have reached the third round for the first time since 2012-13 when they were eliminated by Premier League side Reading.

Crawley have lost all of their FA Cup matches against top-flight opposition - in 2010-11 vs Manchester Utd, 2011-12 vs Stoke and 2012-13 vs Reading.

They just couldn't help themselves.

Image source, MerPolEvertonFC

Image source, EPA

A third-round tie at home to lower league opposition? Same as usual for Chelsea.

This is the seventh consecutive year they've faced EFL opponents at Stamford Bridge at this stage of the FA Cup, and the omens aren't great for Morecambe - the Blues have won all of the previous six.

It's going to be some task for one of the smallest clubs in the football league to knock out Frank Lampard's stars.

Image source, Rex Features

Two-time world heavyweight boxing champion Tyson Fury has a gym at Morecambe's Mazuma Stadium home and Shrimps boss Derek Adams says: "You've got Tyson Fury, who has his gym in the corner of our stadium, a heavyweight in Chelsea against a lightweight in Morecambe.

"Morecambe's waited years for a tie like this. It's fantastic for the town."

Eeva Whybrow: Come on, @MarineAFC !!! Let's cause an upset of the century. Work as a team. Don't stop running until the final whistle blows. @SpursOfficial players are human beings; they can be beaten. Believe in yourself.

Image source, PA Media

Having finished 22nd, 18th, 22nd, 18th and 21st in the last five seasons, an FA Cup trip to eight-time winners Chelsea is a welcome distraction from the rigours of League Two for Morecambe.

This is the club's first appearance in the third round since 2003 but there is naturally sadness none of their supporters will be at Stamford Bridge.

"It's a damned shame. We could have been looking at taking 5,000 in normal circumstances," says Shrimps co-chairman Rod Taylor.

Read about how Morecambe have coped during lockdown here.

Morecambe will be hoping they can spring a big surprise at Stamford Bridge today.

Chelsea are eight-time winners of the FA Cup and reached the final last season.

Morecambe, seventh in League Two, are making their first appearance in the third round since 2003.

Since the Shrimps played Ipswich at this stage 18 years ago, Chelsea have won the competition five times and finished runners-up twice.

Marine keeper Bayleigh Passant nipped to the shop to get beers to celebrate his side's win over Havant & Waterlooville in the last round - still dressed in his kit.

Imagine the scenes if the non-league side do manage to pull off the greatest shock in FA Cup history!

Of course, those six games precede a brilliant tie between Premier League and Northern Premier League Division One North West opposition, which will be shown live on BBC One.

Image source, Getty Images

Premier League side Leeds United make seven changes for their visit to Crawley but Marcelo Bielsa still names a fairly strong team.

Liam Cooper returns from injury at the heart of the Leeds defence while Kalvin Phillips, Rodrigo and Ezgjan Alioski all start.

Crawley make just one change from the side that beat Bolton in their most recent League Two game as Nick Tsaroulla replaces Archie Davies.

Reality TV star Mark Wright, who signed on non-contract terms last month but is yet to make his debut, is on the bench, alongside his brother Josh, who joined Crawley this week.

Leeds XI: Casilla, Davis, Struijk, Cooper, Alioski, Phillips, Shackleton, Hernandez, Poveda, Costa, Rodrigo.

Subs: Caprille, Huggins, Jenkins, Casey, Harrison, Raphinha, Greenwood.

Crawley XI: Morris, Francomb, Craig, Tunnicliffe, Dallison, Tsaroulla, Powell, Hessenthaler, Matthews, Nadesan, Nichols.

Subs: Nelson, McNerney, Doherty, M Wright, Davies, J Wright, Frost, Glach, Waters.

Six changes for Chelsea but it's still a strong side with Timo Werner, Mason Mount and Hakim Ziyech among the starters.

Nineteen-year-old midfielder Billy Gilmour also starts.

Chelsea: Arrizabalaga, Azpilicueta, Zouma, Rudiger, Emerson, Mount, Gilmour, Havertz, Ziyech, Werner, Hudson-Odoi.

Substitutes: Jorginho, Abraham, Pulisic, Caballero, Tomori, Kovacic, Giroud, Chilwell, Anjorin.

This is Morecambe's first game since Boxing Day after a coronavirus outbreak at the club and the League Two club make one change from the side that beat Grimsby 3-1 last time out.

Captain Sam Lavelle is not involved so former Nathaniel Knight-Percival comes into the defence.

Morecambe: Halstead, Cooney, Knight-Percival, Davis, Hendrie, Wildig, Songo'o, Slew, Phillips, Mendes Gomes, Stockton.

Substitutes: Lyons, Turner, Mellor, Diagouraga, Kenyon, O'Sullivan, Leitch-Smith, McAlinden, Gibson.

It's just two changes for Barnsley from the side that lost narrowly to Championship leaders Norwich last weekend. Brad Collins starts in goal and Alex Mowatt returns to skipper the side.

Tranmere manager Keith Hill suggested his side had been affected by Covid-19 in the run-up to this match, after their last game against Colchester was called off.

It's five changes for the League Two outfit with defensive lynchpin Peter Clarke a notable absentee.

Cheltenham make three changes for their meeting with Mansfield, as Chris Clements, Finn Azaz and Liam Sercombe are replaced by Ellis Chapman, Conor Thomas and Andy Williams.

There are two changes for Mansfield, as Corey O'Keeffe and Stephen McLaughlin come in for James Perch and Ollie Clarke.

Image source, Getty Images

Manchester City boss Pep Guardiola told the media on Friday that club record goalscorer Sergio Aguero would, all being well, make his first start since October today.

"Sergio, he's unique, but he's had a tough injury, really tough. The important thing is his mood is exceptional, better than ever," Guardiola said.

"He is an important part of the group, he is incredibly loved, and the important thing is that in the last 10 days or two weeks, his knee's reaction was really good after the training.

"He's going to start and the minutes his performance or knee will dictate. If he can play 90 minutes it will be great, or 60 or 30 minutes will be great."

But he doesn't even make the bench.

Chris Bevan
BBC Sport at Etihad Stadium

There is no Sergio Aguero in Manchester City’s squad to face Birmingham - it was anticipated that the Argentina striker would be fit enough make his first start since October.

It’s still a strong line-up from Pep Guardiola, though. He makes only four changes from the team that beat Manchester United in the Carabao Cup semi-final on Wednesday night - Benjamin Mendy, Kyle Walker, Bernardo Silva and Gabriel Jesus are the players who come in.

Man City XI: Steffen, Cancelo, Dias, Walker, Mendy, Rodrigo, Mahrez, De Bruyne, Foden, Bernardo, Jesus

Birmingham make four changes from the side that lost to Blackburn last weekend. Andres Prieto, Maxime Colin, Jon-Miquel Toran and Scott Hogan all return.

Colin was the last player to score a goal for Birmingham, on 19 December. They have drawn a blank in their three Championship games since.

Birmingham XI: Prieto, Colin, Clarke-Salter, San Jose, Friend, Sunjic, Kieftenbeld, Sanchez, Toral, Leko, Hogan

Alfie Mawson is back for the hosts after a knee injury, while Hakeeb Adelakun and Owura Edwards are named in the squad after returning from loan spells.

Lee Brown and Michael Jacobs return as League One Portsmouth make two changes.

Let's run through the team news for today's six matches at 13:30 GMT.

A challenge for the likes of Morecambe, Crawley, Marine and Newport County is not only to produce a big cup upset today - but also to rival Chorley's post-match rendition of Adele's 'Someone Like You' following their victory over Derby.

What song do you want to see your side singing after victory in the cup today?

Get in touch with those shouts, plus any other thoughts on today's games, via #bbcfootball or text 81111.

BBC Radio 5 Live

BBC Radio 5 Live also have you covered with three live commentaries covering Crawley v Leeds (13:30 GMT), Marine v Tottenham (17:00) and the day's final tie between Newport County and Brighton (19:45).

Manchester City v Birmingham City (13:30) can be followed on 5 Live Sports Extra.