Manchester City were nine minutes away from being dumped out of the FA Cup by League Two Cheltenham but late goals saved their bacon as they rallied to earn a 3-1 win.
Longshots are regularly seen in this part of the world with Cheltenham racecourse just a mile away from the Jonny-Rocks Stadium and Michael Duff's team almost created another one when Alfie May prodded them ahead (59) against a team 72 places above them in the league pyramid.
It looked to be one of those nights in the famous competition as City squandered chances but with just nine minutes to go Phil Foden drew City level (81) before Gabriel Jesus ended the possibility of extra-time with another close-range finish (84).
Ferran Torres added an unfair gloss to the scoreline in added time (90+3) as this was a night all about the work-rate, quality and defensive brilliance from the League Two side.
City now face Swansea in the fifth round.
Southampton: Griffiths (8), Raglan (8), Tozer (9), Boyle (8), Blair (7), Freestone (7), Thomas (7), Clements (7), Azaz (7), Lloyd (7), May (8)
Subs: Long (N/A), Williams (N/A)
Man City: Steffen (6), Garcia (6), Harwood-Bellis (6), Laporte (7), Mendy (5), Fernandinho (6), Doyle (6), Mahrez (6), Torres (6), Foden (8), Jesus (6)
Subs: Cancelo (7), Dias (6), Gundogan (6)
Man of the match: Ben Tozer
How Cheltenham came close to a giant-killing…
Despite grabbing huge plaudits, it could have been a very different narrative for Cheltenham had Jesus found the net inside 30 seconds after being found by Riyad Mahrez.
The visitors were then denied an opener after 12 minutes as Tommy Doyle's cross was half-cleared to Benjamin Mendy and the defender's strike was brilliantly cleared off the line by a diving Ben Tozer.
Goalkeeper Josh Griffiths then came to the fore, making a low save from Torres after some impressive work by Foden.
Jesus headed over soon after but the Robins conjured their own opening after 23 minutes.
May was a pest for the City defence all evening and he latched on to George Lloyd's header but Zack Steffen turned his low effort behind.
The Robins remained confident on the ball and resolute in defence, forcing Pep Guardiola's side to shoot from distance and got to half-time level.
Cheltenham needed Jesus to miss a glorious chance after 53 minutes to keep the scores level. Foden's cute through ball sent the striker clear but with just Griffiths to beat he hit the outside of a post from 15 yards.
City had dealt with Cheltenham's aerial threat until Tozer sent a long throw into the box on 59 minutes. This time the visitors failed to deal with it as they allowed May to run in unchecked and he poked home from close range after Cheltenham had won the first ball.
A classic FA Cup shock was now on the cards and Guardiola sent on Ruben Dias, Ilkay Gundogan and Joao Cancelo in search of a way back into the match.
It forced City to up the tempo and Griffiths saved from Mahrez after Foden slipped the forward in.
An equaliser did not look likely but City finally overcame their hosts in the final 10 minutes.
Foden had been their best player and he levelled with nine minutes left, volleying in Cancelo's cross.
Jesus then completed the turnaround three minutes later as Cheltenham tired before Torres added an undeserved third for the Premier League title favourites.
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What the managers said
Manchester City boss Pep Guardiola said: "We learned to suffer and at the end the quality made the difference. We won the game and we are happy to win this game in this type of competition.
"We knew how tough it would be and the response from the players was magnificent.
"The chances we had a 0-0 were so clear and if we scored it would have been very different.
"They had a fantastic team, what they do they do really well. They defended well, May is an exceptional player. Every throw is more important than a corner or a free-kick.
"In the FA Cup this is why it's nice, everyone can beat everyone. I don't have any regret over how we were behaving and the way we played. We scored three magnificent goals.
"We reacted so well, in this competition it's not the first time a Premier League team has suffered. We suffered well."
Cheltenham boss Michael Duff said: "I thought it was an incredible performance, I'm really proud of the players. Maybe we have stepped out of the racecourse's shadow for five minutes.
"The last thing I said to them was 'can you walk off the pitch with your shoulders back proud of yourself?' You can't guarantee the result but we said 'can you make a mark in a positive way?' Pep and the players know they have been involved in a half-decent football match.
"We could have been 1-0 down after 17 seconds and there was a bit of nerves because they can put nine past better teams than us.
"I don't think the lads deserved to concede a third goal, we have lost to the best team in the world right now and the players have given an incredible account of themselves.
"There's a tinge of disappointment but the lads will get unbelievable attention so I told them to enjoy the moment but to turn up on Monday ready to go to work because we have Oldham at home (on Tuesday)."
- Manchester City have won 10 consecutive games in all competitions for the first time since a run of 11 between August-October 2017.
- May's opener for Cheltenham was the first goal Manchester City had conceded in 509 minutes of action in all competitions, since Callum Hudson-Odoi's strike for Chelsea at the start of the month.
- Foden is Manchester City's top scorer in all competitions this season with nine goals in 25 appearances, one more than he netted in 38 games last season (8).
FA Cup 2020/21 - key dates and draw
The FA Cup schedule has been confirmed, with the final set to take place at Wembley on Saturday May 15.
There will be no replays this season to help ease fixture congestion.
- Fifth round: Wednesday February 10
- Quarter-finals: Saturday March 20
- Semi-finals: Saturday April 17
- Final: Saturday May 15