Marcelo Bielsa might have been able to tell everyone this before the game but penalties were required to separate Southampton and Derby in their third-round FA Cup replay. It was Frank Lampard’s side who held their nerve and go through to face Accrington Stanley in the fourth round after Nathan Redmond was the only man to miss in the shootout, the winning kick struck home by the unlikely figure of Richard Keogh.

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“Ready for my presentation everyone?” said Lampard as he walked into his post-match press conference, making light of Bielsa’s extraordinary 70-minute press conference earlier on Wednesday, in which he revealed he had not only Derby’s training sessions watched but every team they have faced this season.

When it was put to him that Bielsa gave the impression he knew more about Derby than their own manager, Lampard said: “Well‚ he gave an impression of himself. I haven’t seen Pep Guardiola give that. I haven’t seen Jürgen Klopp give that. Pochettino give that. They do that sort of thing behind closed doors but they don’t do it to the public. It surprised me, definitely. It’s incredible.”

Back at St Mary’s, Derby repeated the trick of the first game, coming from 2-0 behind once more to force extra time and ultimately spot-kicks. Southampton surely thought they had a fourth-round place in the bag after goals from Stuart Armstrong and Redmond, only for the Liverpool loanee, Harry Wilson, to inspire Derby’s comeback, firstly with a goal of his own, then by crossing for Martyn Waghorn to equalise. “I think if you have a 2-0 lead twice over Derby and can’t winthe game,” said Ralph Hasenhüttl, “you don’t deserve to be in the next round.”

Facebook Twitter Pinterest The Derby players celebrate after Richard Keogh’s winning penalty put Frank Lampard’s side through. Photograph: Dan Mullan/Getty Images

The first half was a pretty grim exhibition but, when good bits of football did poke through the mist of mediocrity, they were from Derby. One delicious move involved a Matthias Sammer-esque carry out of defence from Keogh, followed by a couple of flicks and back-heels among the forwards, but its deserved finish did not arrive when Mason Mount skied his shot from the edge of the box. Otherwise it was tedious: pity the poor Bielsa assistant who had to compile a dossier on this one.

But they sat up straight on 38 minutes, when Derby took the lead. Or, at least they thought they had. Tom Huddlestone slid a fine pass into the box for Waghorn, who laid it off for Craig Bryson to finish neatly. However, VAR was called for and after the sort of forensic, frame-by-frame examination only previously seen by conspiracy theorists watching the Zapruder film, it was determined that the bottom half of Waghorn’s leg was offside. No goal. In the stands the Derby fans sang “Fuck VAR!”but afterwards Lampard was more sanguine.

“I think we’ll have to get used to it,” he said. “I don’t mind as long as they get the decision right. Was it right? I haven’t looked closely enough but it looked like it was millimetres.”

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Then, after the boredom of the first period came a glut of goals in the second. Southampton went ahead after 67 minutes when Shane Long’s header was blocked on the line, only for Armstrong to swoop in and nod the loose ball home.

Two minutes later it was two. Redmond timed his run through the middle of the Derby defence perfectly and on the very edge of the defensive line collected Jack Stephens’s pass and delicately chipped over the advancing Kelle Roos.

Derby were given hope with 15 minutes remaining. Wilson took a free-kick from the right corner of the box, zipped it into the middle at pace and it went past everyone into the net. “I was just about to take him off,” said Lampard, his second thoughts proving crucial a few moments later. Wilson curled over a cross from the right, and Waghorn found space between two defenders to head into the top corner.

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Extra time was required, meaning the Prime Minister’s statement in Downing Street was relegated to BBC2 as BBC1 continued to show the game. “They deserve those moments,” said Lampard, of his players. “Theresa May will have many a moment coming up over the next few weeks, I would say.”

After a cagey extra 30 minutes came penalties. Redmond was the only player to err, shooting well wide after opening up his body and aiming for the top corner. The other eight kicks were flawless, Derby rushing to celebrate with Keogh at the end of a long night.