Good night!published at 23:01 GMT 16 January 2019
Just the 172-mile drive back to Derby for the away fans then. At least they've got a win!
Drive safe all. That's a wrap from us.
See you on Saturday?
Watch game on BBC One and listen on BBC Radio 5 live
Keogh scores winning spot-kick to set up tie with Accrington in round four
Saints led 2-0 through Armstrong and Redmond strikes
Wilson free-kick reduces the deficit before Waghorn heads in
Derby's Bryson earlier had finish ruled out by VAR for narrow offside call
Tom Rostance
Just the 172-mile drive back to Derby for the away fans then. At least they've got a win!
Drive safe all. That's a wrap from us.
See you on Saturday?
Derby win on penalties
Southampton
Image source, PASouthampton manager Ralph Hasenhuttl speaking to BBC Sport: "Congratulations to Derby County. When they fight like they did in the two games, they deserve to go through to the next round.
"We didn't deserve to win. We had a few chances and didn't get the goal. We have given the lead away two times so it was very disappointing.
"It was very frustrating. We were not very good in the first half so made changes to the system at half-time. Second half we were much better and played well for the two goals.
"But they got a goal from a set-piece and you could feel everybody thinking about the first game and getting a bit nervous. The opponent was in the right place to score a second time. and both sides had less power in extra-time. We still had chances to win it but didn't take them.
"I think Shane Long can play on Saturday. We don't have a problem scoring goals but if you keep conceding two goals then it's too much.
"We've played 120 minutes and play on Saturday, but we have a few fresh players to come in to the team and we'll come back."
Derby win on penalties
Image source, ReutersDerby County’s Harry Wilson has scored eight goals from outside the box in all competitions this season, at least twice as many as any other player in the top four tiers of English football in 2018-19.
Five of those eight have been from direct free-kicks.
Derby win on penalties
Image source, Getty ImagesDerby County have now progressed from all three of their penalty shootouts in the FA Cup, all coming in third round replays (also against Sheffield Wednesday in 2007-08 and Millwall in 2009-10).
Derby win on penalties
What a game!
Here's all of the key moments...
More from Derby manager Frank Lampard: "I'm very happy, you have to be proud when your team plays like that against a Premier League team. We've done that a few times this season.
"The FA Cup is magical, to do that makes me proud. At 2-0 down it was easy to give up and they didn't. I've got a really good dressing room with great characters. They wanted to play, to run when fatigue kicks in and we thoroughly deserved to win the game.
"I'm delighted for Richard Keogh. Everyone at this club knows how important he is, the club means so much to him. He drives the squad for me every day on the training ground. He deserves that moment.
"He asked to take one. I know he's got quality, he is a man of strength, the sort of man you want to take that.
"Harry Wilson was brilliant. He's been out for a few weeks and he was spot on. He's important for us and we need him fit."
Here's the winning moment...
Derby win on penalties
BBC One
Derby manager Frank Lampard on BBC One: "We've had two games against Southampton and a tough patch in the league, playing some really good teams, so the lads have been working so hard and they did it again tonight.
"It takes a lot to come back against Premier League opposition and show the fight, and the bravery on the ball. I thought we were outstanding through the game. Some of the football in the first half was brilliant.
"It's a tough turnaround for the weekend and Accrington in the next round - it's the FA Cup, it's magical, look at the fans who have travelled.
"A big thank you to the fans because it's half past 10 already. They're going to get back to Derby at whatever time and they're probably working tomorrow too so a big thanks to them because they helped us get over the line."
Derby win on penalties
BBC One
Image source, Getty ImagesDerby manager Frank Lampard on BBC One: "I'm delighted for the team and the squad. The work rate they put in there, having to come through VAR going against us in really small margins, they worked so hard and they were great penalties at the end and great courage from the lads.
"They were winners today going into the penalties anyway, and the way they took them showed great strength of character so I'm really proud of them."
BBC One
Image source, PADerby captain Richard Keogh on BBC One: "It's an amazing feeling. Against all the Premier League teams we've played this season we've shown our quality and again we showed our resilience to come back against a good team.
"VAR going against us was crazy. We had a big meeting about it before, the referee talked us through it, and then that happens against us. But we stuck in there and played really well."
#bbcfootball or 81111 on text (UK only)
Image source, Getty ImagesGreat to see Frank Lampard spending so long applauding the Derby fans after the penalties tonight. Big journey on a Wednesday night. Respect to both.
Callum Simpson
Jermaine Jenas
Former England and Tottenham midfielder on BBC One
Derby have played Manchester United, Chelsea and Southampton this season in the cups and haven't looked out of place in any of them.
Frank Lampard thanks the fans who have come down to Southampton - 'It's half 10 already, what time are they going to get home tonight? And then have work in the morning...'
Southampton 2-2 Derby
Danny Murphy
Former Liverpool and England midfielder on BBC One
For a Championship side to come back from 2-0 down, show the desire and quality... good substitutions, good attitude, good team, I'm really pleased for them.
Southampton deserved credit too but, for me, the best team went through.
Frank Lampard won the FA Cup four times as a player and he now soaks up the acclaim of the 1,000+ away fans. Who says nobody cares about the FA Cup anymore?
Oh yeah. Nearly everyone...
It's not the case though is it? A win is a win!
Image source, Getty Images#bbcfootball or text 81111 (UK only)
Bielsa knew where every single Derby penalty was going.
Nigel, Battersea
Fair play Derby County - 2-0 down against Southampton twice, and now through on penalties!
#bbcfootball or text 81111 (UK only)
Day Anthony: Nathan Redmond just passed the ball for the first time tonight. To a fan in row F.
Image source, ReutersDerby will face Accrington in the fourth round of the FA Cup!
Richard Keogh
He does win it! Slots it in superbly and Derby have a Premier League scalp.