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17:58 GMT - GOAL! Tammy Abraham finishes well to hand Villa the lead over Newcastle.
Major questions over an offside and Abraham did stray, but no VAR at this stage of the competition means it stands!
17:45 GMT - KICK-OFF! Aston Villa versus Newcastle is underway - follow the match here
17:40 GMT - Mansfield first-team coach Andy Garner, speaking to TNT Sports: "We said that to them at half-time, that we didn't think there was anything to fear. We were a little disappointed in the first half with how much we gave the ball away, especially in the final third a bit sloppy at times.
"We said, 'let's get back into this game' and we believed we could."
17:37 GMT - FULL-TIME! A James Bree header in extra-time earns Southampton a 2-1 win over Leicester and a place in the fifth round.
17:27 GMT - Recap this afternoon's action as Manchester City dispatched League Two's Salford and League One outfit Mansfield shocked Premier League side Burnley.
Read more: Guehi scores as Man City edge Salford in FA Cup, Burnley upset by Mansfield
17:22 GMT - GOAL! Southampton lead Leicester 2-1 in extra time as James Bree heads in at the back post.
17:10 GMT - Next up, attention will turn to Villa Park - the scene of Aston Villa's clash with Newcastle, which kicks off shortly at 17:45 GMT.
Meanwhile, it's still 1-1 between Southampton and Leicester heading into the second half of extra time.
16:56 GMT - FULL-TIME! The whistles are blowing in the afternoon fixtures.
FT: Manchester City 2-0 Salford
Latest: Southampton 1-1 Leicester (extra time)
16:51 GMT - GOAL! Norwich seal the deal with Mohamed Toure continuing his fine scoring form.
16:48 GMT - The lineups are in for Aston Villa against Newcastle, which kicks off at 17:45 GMT.
16:42 GMT - GOAL! Norwich are 2-1 up against West Brom thanks to Benjamin Chrisene's finish.
16:39 GMT - GOAL! New arrival Marc Guehi gets his first for his new club as Manchester City finally double their lead against Salford, who have given a good account of themselves.
Elsewhere, the shock could be on as Louis Reed puts Mansfield ahead after a well-worked goal makes the score 2-1 with around 10 minutes left.
16:13 GMT - GOAL! League One Mansfield have equalised away at Burnley!
Rhys Oates pulls the underdogs level against the Premier League side. Is an upset on the cards?
16:10 GMT - GOAL! Leicester are level after a fine overhead kick from Oliver Skipp.
16:02 GMT - We're back underway in all four games.
16:00 GMT - West Ham boss Nuno Espirito Santo, speaking to BBC Sport: "We knew it would be tough. We were able to contain them in the aspect of set pieces and the throw-ins. We did that in the first half, and then in the second half we came on strong, creating chances.
"Then Summerville gave us a hand. He is in a good moment, he is helping out the team. This is what we expect from them.
"This is a magical competition. It is unique. We have a lot of respect. Today we came through, the draw is Monday. We go day by day."
15:50 GMT - HALF-TIME! The whistle blows around the grounds in the FA Cup.
15:46 GMT - GOAL! Southampton are ahead against Leicester after Cyle Larin slots home the penalty.
15:33 GMT - GOAL! Paris Maghoma has put Norwich ahead against West Brom.
15:22 GMT - GOAL! Burnley lead against Mansfield after Josh Laurent pokes home.
15:18 GMT - Manchester City have had 92 per cent possession over the opening 15 minutes of this game. Imagine chasing after that.
15:06 GMT - GOAL! Manchester City take an early lead against Salford after what appears to be an own goal.
Omar Marmoush will want it but it's an Alfie Dorrington own goal. It's 1-0 already to City.
15:01 GMT - We're getting underway in those matches now.
14:59 GMT - With West Ham safely through, we're straight in with more FA Cup fourth round matches:
14:56 GMT - FULL-TIME! The Hammers scrape through to the fifth round with a narrow 1-0 win against Burton after extra time.
Read more: Summerville's extra-time strike spares West Ham from Burton upset in FA Cup
14:56 GMT - The players have got into a scrap as the final whistle looms. Burton have a free kick and the keeper is up.
14:55 GMT - Another chance goes begging for Burton as Tyrese Shade hits the side netting.
14:52 GMT - Lofthouse narrowly places the ball wide with time almost over. Burton go close to a late leveller!
14:48 GMT - Summerville nicks the ball and has a real chance to seal West Ham's place in the next round, but he misses the target.
Burton respond by throwing more men forward.
14:45 GMT - We have about 10 minutes left of extra time, and Burton are on the front foot now.
14:35 GMT - At 22 years and 155 days, Freddie Potts is the youngest player to be sent off for West Ham since Callum McNaughton in August 2011 (19y 303d versus Aldershot Town).
14:28 GMT - RED CARD! West Ham are down to 10 after Freddie Potts is shown his marching orders for a heavy challenge.
That's the first of the 22-year-old's career.
No VAR, remember, but it looks like the right call.
14:21 GMT - GOAL! At long last we have the breakthrough, and it goes to West Ham.
Crysencio Summerville scores a fine solo goal to continue his fine run of form for the Hammers.
14:17 GMT - We're underway in extra time.
14:12 GMT - FULL-TIME! It ends goalless and we head into extra time between Burton and West Ham.
Probably not what Nuno Espirito Santo wanted, with his side's Premier League run-in to consider.
14:00 GMT - Burton Albion are yet to have a shot in the second half, while West Ham have had 10.
We're into the last 10 minutes, and we'll go to extra time if things stay the same.
13:36 GMT - West Ham have already had three times as many shots in the second half of this match (six) as they did in the entire first half (two).
13:22 GMT - The second half is underway.
13:08 GMT - There goes the half-time whistle.
Not too much to report, but Burton are well and truly in this one.
12:45 GMT - Still goalless at Burton.
This is the fourth time this season West Ham have failed to have a shot in the opening 30 minutes of a match.
12:15 GMT - We're underway between Burton and West Ham.
12:12 GMT - Burton's Tyrese Shade is the top scorer in the FA Cup proper so far this season, with all five coming in his last two appearances. His teammate Fabio Tavares has also been directly involved in five goals in the competition this season (three goals, two assists), but he starts on the bench today.
12:08 GMT - Chelsea boss Liam Rosenior was delighted with the attitude of his players for their FA Cup fourth round win at Hull City on Friday night.
Returning to the club which he served both as a manager and player, Rosenior saw his Chelsea players earn a 4-0 win on the night, with Pedro Neto scoring a hat-trick.
"I'm very lucky to have such talented players and what I'm really realising quickly is that they are not just good players, they’re outstanding professionals.
"I felt it was a really professional performance tonight against a very good team who are pushing for the Premier League."
Read more: Rosenior pleased with 'professional' Chelsea FA Cup win against Hull
12:06 GMT - West Ham are showing plenty of respect for opponents Burton given the strength of their lineup today:
12:00 GMT - Welcome aboard this weekend's FA Cup Football Tracker!
We have seven matches in the pipeline today, beginning with League One's Burton hosting Premier League side West Ham first at 12:15 GMT.
