It was a hard fought game with Saints having to come from behind to force a win against a Coventry side who came at them with all guns blazing, but Saints battled right to the final minute of extra time injury time to make sure they were in the 5th round draw.
Ralph Hasenhuttl has usually kept the foundations of his first choice XI for the FA Cup, but for this one he made wholesale changes, although such is the depth of the squad at the moment, only debutant Thierry Small had no real first team experience and all of his fellow outfield players had been first choice players at some point.
Ralph had gone for three at the back, but it looked a bit shaky with Yan Valery inexperienced in this role, Lyanco still finding his way in English football and Jack Stephens being the trio entrusted.
Thierry Small and Tino Livramento were employed as wing backs with Ibrahima Diallo joining James Ward Prowse in the centre, up front Shane Long was joined by Adam Armstrong with Theo Walcott seemingly playing a free role.
From the start it was clear that the Sky Blues were here for a game and although we looked fairly strong early doors, the warning signs were there.
They weren't heeded and just as Saints looked like they had a hold on the game Coventry popped up and scored, for the rest of the half we huffed and puffed but rarely threatened.
We had to re jig in the 34th minute when Lyanco had to go off through injury and with no recognised central defender on the bench that meant adapting with Nathan Redmond the replacement.
Half time saw two changes, on came Walker Peters on for Small, who had had a promising if not explosive debut and would probably have stayed on longer if it hadn't been for the issues at the back and on the other side Stuart Armstrong came on for his namesake Adam and we re jigged the formation a little.
Just after the hour came the breakthrough and it was a swerving dipping shot from distance that flew in from Stuart Armstrong that drew us level, it was a shot that JWP, Matt Le Tissier and Rickie Lambert would all have been proud of and is right up there as one of the greatest goals at St Mary's
On came Armando Broja for Walcott and surely now Coventry would be breached again, that would not be the case though and despite dominating possession we couldn't score again and it was extra time.
Coventry dug in, but with only 8 minutes to go Kyle Walker Peters tucked the ball away to give Saints surely the winning goal.
But the Sky Blues hadn't read the script and kept going as if their lives depending on it, as injury time loomed the warning signs were there, a free header flashed just wide when it looked easier to score and then came Willy Caballeros moment, he saved once, he got up and saved again, at the third attempt he almost blocked again, but the Coventry man was clearly offside as the ball was forced home.
But Caballero had done his job in not giving up what looked like lost causes and these saves and a couple of others early in the game make a case for him to be man of the match.
But with the final whistle blown, the nature of the job doesn't matter, all that matters is that we are in the 5th round draw.
In many respects it was a pleasing result, what was in effect a virtual second string side could beat a good Championship side and that bodes well for the Premier league, i have always said that it is not just about the eleven out on the pitch in any game, it is about who you have on the bench as they are the people who you need to go to, either to change the game or to shore it up, last season too often our bench was full of kids, this season it is different and we have options.
It wasn't all positive though, there was still too much slackness on show, sometimes we have to learn when to put our foot through the ball and when to make a simple pass rather than a difficult one.
Again a team performance with a couple of outstanding contributions, namely Caballero and that stunner from Stuart Armstrong, some were critical of Ralph in the pub after saying he changed the team too much, but with two games in the next 7 days coming up, he needed to conserve the energy of the bulk of the team that will face both Spurs & United.