SAINTS produced a performance to be proud of but ultimately fell to a 3-0 defeat at the hands of a young Liverpool side in the FA Cup fifth round.
Lewis Koumas and Jayden Danns, both 18 years old and sons of former professionals, scored their first goals for the Reds in either half.
Danns added his second just ahead of four minutes of added time to rubber stamp the victory and progression to face Manchester United in the quarter-final.
Russell Martin's side had a succession of chances at 0-0 and at 1-0 down but could not find their clinical edge in front of 5,500 travelling supporters.
Concern followed as substitute Kyle Walker-Peters was brought off in the aftermath of the second goal after less than 20 minutes and went straight down the tunnel.
Saints had a task to put behind them three defeats in four in the Championship to visit the side top of the Premier League.
Martin made eight changes from the XI that were beaten by Millwall at St Mary's, with only Jack Stephens, Jan Bednarek and Joe Aribo keeping their places.
Liverpool and Jurgen Klopp, fresh off their EFL Cup win at Wembley on Sunday, were themselves fielding a patched-up team due to injury concerns.
There was no Mohamed Salah or Darwin Nunez, with five academy youngsters starting - although club captain Virgil Van Dijk was ready.
Two, Koumas and James McConnell, started against Southampton's under-21s in Premier League 2 at Snows Stadium earlier in the season.
Saints earned admiration for their commitment to playing out the back and - for the most part - it was pretty and effective.
Sekou Mara scored with a confident finish low into the bottom right corner in the first minute but the dream start was ruled out for offside.
Kamaldeen Sulemana hit the post after Aribo rolled through the Liverpool half and then Mara had two big chances from inside the area saved by Caoimhin Kelleher.
The second popped to the Frenchman at the back post after Sam Edozie's prod was blocked, but Kelleher advanced quickly - and Mara was offside anyway.
Former Saints target Cody Gakpo looked to punish a misplaced Ryan Manning pass out the back but Liverpool's first big opportunity rolled into Joe Lumley's hands.
Another chance went begging before half-time after Kamaldeen drove into the box but hit the keeper while Lumley expertly denied Harvey Elliott.
The next one was not to be wasted - Koumas, son of former Wales international Jason, converted from the edge of the area via a deflection.
Martin refrained from making changes during the break but Klopp pulled van Dijk, who scored the winning goal in the cup final, for Ibrahima Konate.
More chances were missed by Kamaldeen and Gakpo as the open contest continued before the managers made their first round of double-substitutions.
World Cup winner Alexis Mac Allister was added for the hosts but it was Southampton's Shea Charles with the next big opening, firing into the side netting free in the box.
They were made to pay for a lapse in possession as substitute Will Smallbone misplaced a pass behind Manning for the Reds to take full advantage.
Elliott played in Danns and the teenager lofted Lumley with full composure to end the tie as a contest after 73 minutes.
The young Englishman made it a brace when Conor Bradley's shot was parried into his path in what was a good initial save by Lumley.
Saints fans stayed to full-time in their numbers and applauded the team off the pitch, alongside a rendition of 'Oh when the Saints'.
Liverpool: Kelleher; Gomez, van Dijk (Konate, h-t), Quansah, Tsimikas; McConnell (Mac Allister, 62), Clark, Elliott (Nyoni, 78); Bradley, Koumas (Danns, 62), Gakpo (Gordon, 89)
Unused subs: Adrian, Diaz, Scanlon, Nallo.
Saints: Lumley; Bree (Walker-Peters, 58 (Harwood-Bellis, 74), Bednarek, Stephens, Manning; Charles, Rothwell (Smallbone, 69), Aribo; Kamaldeen (A Armstrong, 58), Edozie (Adams, 69), Mara.
Unused subs: McCarthy, Amo-Ameyaw, Meghoma, Dibling.
Booked: Manning.
Referee: Craig Pawson.
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