And for their next trick, Liverpool advance into the FA Cup quarter-finals thanks to two 18-year-olds who were due to be playing Leeds in the FA Youth Cup semi-final on Thursday and fielding the youngest player to appear in the competition in the club’s ­history. The Liverpool ­academy’s pursuit of the quadruple goes on.

Lewis Koumas, son of former ­Tranmere and Wales playmaker Jason, and Jayden Danns, son of former Crystal Palace midfielder Neil, scored the goals that booked the Carabao Cup winners a visit to Manchester United in the last eight.

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“We haven’t won a trophy, since Sunday afternoon,” sang the Kop after witnessing two 18-year-olds score in the same game for Liverpool for the first time. Not content with winning the first trophy of the season with inexperienced youngsters three days earlier, Jürgen Klopp also introduced 16-year-old Trey Nyoni for his record-breaking FA Cup debut for good measure.

Southampton created more than enough chances to have derailed Klopp’s hopes of finishing his Liverpool reign with another trip to Wembley. But they lacked the quality, conviction and composure in front of goal shown by Koumas on his full Liverpool debut and Danns in scoring his first two goals for his boyhood club.

“It’s like the new darts sensation,” said Klopp, unexpectedly comparing Liverpool’s kids to Luke Littler. “Tonight it is fine [to praise them] but tomorrow leave them alone, they have a lot to learn. They are exceptional talents.

“Of course it is not natural that an 18-year-old [Danns], as calm as you like, comes into that situation and chips the ball in. The future doesn’t look that bad. Maybe people don’t forget that when the transfer window opens – don’t close the door on these boys. But Joe Gomez is the real story. Joe saved our lives and the kids kept us in the competition. I couldn’t respect him more.”

Gomez anchored midfield with two other teenagers, Bobby Clark and James McConnell, either side. Klopp again had to turn to youth with Ryan Gravenberch and Wataru Endo having swelled the ranks of the injured. Conor Bradley and Jarell Quansah also started with Koumas making his full debut on the left of Liverpool’s attack.

The Southampton manager, Russell Martin, rang the changes out of desire, not necessity, with an eye on the club’s promotion prospects. Resting eight players from Saturday’s home defeat by Millwall may have invited criticism but it was counter-acted by his team’s impressive display. It should have brought a comfortable lead before Liverpool had found their way into the tie.

“The start was all over the place,” admitted Klopp. “They tried to press because they know I want them to press, but the timing was horrendous.”

Kamaldeen Sulemana set the pattern for Southampton’s wasteful night when placing an early shot against the base of a post. Sékou Mara, who converted past Caoimhin ­Kelleher after 29 seconds but was clearly offside, had an excellent chance seconds later when dispossessing McConnell. His low shot was well saved by the Liverpool goalkeeper.

Joe Rothwell weaved his way into space inside the area but shot well wide of Kelleher’s goal. Sulemana had another fine opportunity when his pace took him away from Bradley and Quansah and left him with only the Republic of Ireland international to beat. A tame, side-foot finish straight at Kelleher ensured he did not.

Liverpool punished the visitors’ profligacy for a first time when Koumas marked his debut with a moment he will never forget. Receiving Clark’s pass on the corner of the area, the teenager cut across Jack Stephens and dispatched a low shot that flew into the bottom corner via a slight deflection off Jan Bednarek. Goalkeeper Joe Lumley was rooted to the spot.

Southampton continued to create the clearer opportunities until fading in the final 15 minutes and continued to squander them. Sulemana, Bednarek, Joe Aribo and Shea Charles all missed chances to equalise before Liverpool put the tie beyond them.

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There was an inevitability to the next round of punishment, in terms of the quality of Liverpool’s second goal and the age of the scorer. It stemmed from a mistake by Southampton substitute Will Smallbone who played a stray pass straight to Harvey Elliott.

Elliott, a relative veteran of this Liverpool team at 20 years of age, released Danns with a perfectly weighted pass and the teenager dinked a superb finish over the advancing Lumley for his first senior goal.

Danns’s second arrived after Lumley parried Bradley’s shot back into the danger zone and the striker reacted quickest to convert into an empty net. “To come on and score at the Kop end is unreal, it doesn’t feel real to me,” said Danns. “It feels like I’m in a movie.”