Southampton progressed to the last 16 of the Carabao Cup on penalties after an enthralling tie finished 2-2 at Bramall Lane.
Saints had trailed to Enda Stevens’s early opener, before turning the tide through first Southampton goals for Ibrahima Diallo and Mohammed Salisu, only for Oli McBurnie to force spot-kicks.
James Ward-Prowse, Ché Adams and Diallo all scored from 12 yards, while Armando Broja was denied.
But two saves from Fraser Forster put Saints in command and Oriol Romeu made no mistake with the decisive kick to send the visitors through.
Ralph Hasenhüttl is enjoying the options at his disposal this season, and Saints’ strength in depth was clear from the nine changes the manager made from Saturday’s hard-fought draw at Manchester City.
Only Nathan Redmond and Romeu remained, with the latter captaining the side in the rare absence of James Ward-Prowse, who was among the substitutes.
Hasenhüttl handed a debut to Lyanco alongside Salisu at the heart of the defence, while there were also starts for Nathan Tella and Broja, as the pair staked a claim to earn their first league starts of the season.
Saints, in their yellow and blue away kit, started brightly, with Romain Perraud forcing a save from Wes Foderingham in the very first minute, but United have taken seven points from their last three Championship games and scored 11 goals in that time.
That confidence, seemingly restored after relegation from the Premier League, was evident as Jayden Bogle raced to the byeline and cut the ball back for Stevens to sidefoot home the opener, wrong-footing Forster as he shot back across the keeper.
The pacey Oli Burke then surged into the box and was only defeated by the angle, poking the ball beyond Forster’s far post as the Blades looked sharp.
This was about to turn into a very watchable first half, as Saints responded with some lively wing play from Tella, whose driven cross was somehow steered wide by Diallo, who could only have been caught out by the speed of the cross.
But the Frenchman would soon make amends with his first goal in English football. After Lyanco headed over a Nathan Redmond corner, Romeu crossed for midfield partner Diallo to guide a well-placed header into the bottom corner, just out of Foderingham’s reach.
Saints seemed to have gained the initiative, but Lyanco was caught out by the lively Iliman Ndiaye, who inadvertently nutmegged Salisu and seemingly had the goal at his mercy only to send his shot past the far post from six yards.
An eventful half for the Brazilian took another twist when he was booked following an aerial clash with McBurnie, who received the same punishment.
The interval prompted changes for both sides, as Ward-Prowse replaced Redmond, pushing Romeu back as Hasenhüttl switched to a three-man defence.
But it was United’s substitutes, Rhian Brewster and Ben Osborn, who combined for a glorious chance as Forster denied Osborn with just enough of a touch off his legs to keep Saints on level terms.
It proved an important stop, as Saints soon took the lead for the first time in the match. Tella’s quickly-taken corner caught the hosts napping, as the youngster combined with Ward-Prowse and fizzed in a low cross that Salisu turned in at the near post like a seasoned marksman.
Saints seemed to have control of the tie for the first time, but United fought back to level the scores again midway through the second half.
A loose pass from Lyanco conceded possession and Osborn’s cross was clinically volleyed in by McBurnie at the far post, as the Brazilian was punished for his mistake.
The introduction of Jan Bednarek in Lyanco’s place 15 minutes from time saw Saints revert to a back four, with Diallo pushing forward and Tella partnering Broja up front.
Adams, with four goals in his last three games against his former club, was summoned for Tella with 10 minutes to go – perhaps with penalties in mind.
It looked an inspired decision when Adams was picked out by a brilliant cross from Perraud, only for Foderingham to reach out and somehow keep the striker at bay with a save that brought a standing ovation from the home fans.
The former Blade went close again when Broja led a one-man breakaway down the right and crossed low, but this time it was just fractionally beyond the stretching substitute, ensuring spot-kicks would be required to separate the sides.
Ward-Prowse stepped up first and scored emphatically, as did Adams, but Brewster and Broja were both denied, leaving the scores level after three kicks each.
When Diallo scored, calmly, and Forster thwarted McBurnie, it was left to Romeu to roll in the winning penalty as Saints squeezed through.