Southampton cruelly exited the Carabao Cup on penalties at Stamford Bridge after a magnificent performance with a much-changed side.
Saints gave as good as they got in the 90 minutes despite making nine alterations against the European champions, who took the lead through Kai Havertz’s header on the stroke of half-time.
The visitors responded soon after the restart through Ché Adams’s first goal of the season, and had chances to win the tie before penalties.
Both sides had gone the distance in the previous round, but it was Chelsea who did so again, prevailing 4-3 on spot-kicks after Theo Walcott was denied by Kepa Arrizabalaga and Will Smallbone blazed over.
Ralph Hasenhüttl promised changes and stuck to his word, with only two survivors from Saturday’s 2-2 draw against Burnley in the Premier League.
The pair to keep their places were Mohammed Salisu and Ibrahima Diallo – Saints’ scorers at Sheffield United in the last round – with Lyanco, Stuart Armstrong and Nathan Tella among those to come in.
Chelsea had scored from an early corner in the recent league meeting between the clubs and threatened to do so again inside six minutes.
Ross Barkley, who made a big impact as a substitute that day, delivered a corner that was met by an excellent header from Saúl Ñiguez, sending Fraser Forster flying through the air to make a spectacular one-handed save high to his left.
Hasenhüttl had taken the opportunity to change more than just personnel, matching up Chelsea’s 3-4-3 formation, with Kyle Walker-Peters and Moussa Djenepo operating as wing-backs, Yan Valery as the third centre-back, and Tella and Adam Armstrong flanking Adams in attack.
For the most part Saints were containing their hosts, who currently top the Premier League, but Havertz twice threatened to make the breakthrough, rifling one shot narrowly wide from distance before stinging the palms of Forster from a tight angle.
Diallo was booked in between those sights of goal for pulling back Mateo Kovačić as the Blues eyed a counter-attack that never materialised.
Saints’ first notable chance arrived on the half-hour mark when Walker-Peters darted between two defenders and the ball ran loose for Stuart Armstrong to strike, but his shot was smothered by Kepa via a slight deflection.
Whilst Hasenhüttl’s side had struggled to create chances, they had done a fine job of restricting their hosts, which made the manner of Chelsea’s opener doubly frustrating.
With just 60 seconds to play in the first half, Hakim Ziyech delivered an outswinging corner from the left met by a thumping downward header from Havertz that bounced beyond Forster’s dive.
Discounting the 15-minute interval, Saints were level again in the blink of an eye.
Starting the second period on the front foot, Valery played in Walker-Peters, whose low shot escaped the grasp of Kepa, inviting Adams to swoop in and score his first goal of the season and perhaps the easiest of his entire career.
Smelling blood, Saints kept pouring forward with admirable self-belief. Adam Armstrong shot optimistically over from long range, before trying his luck from a more presentable position, whipping a low one towards the far corner that had to be pushed aside by the diving Kepa.
At the other end, Havertz jinked inside Lyanco only to be denied by Forster’s legs, before the keeper dived bravely at the feet of Barkley and later tipped over a dipping free-kick from Reece James as the cup tie really came to life.
Thomas Tuchel’s decision to call on England duo Mason Mount and Ben Chilwell midway through the second half was testament to the job Saints’ much-changed line-up was doing, while Hasenhüttl withdrew Tella and goalscorer Adams as Walcott and Shane Long entered the fray.
The substitutions gave Chelsea a lift, and Havertz was trying to pick out Mount when he cut the ball back from the left, but instead it ran through kindly for Ñiguez to strike from 20 yards, who was only just off target.
Then the Spaniard tested Forster from even further out with a brilliantly-placed curling effort, but the keeper was there in plenty of time to frustrate him again.
Further changes followed with the introduction of Oriol Romeu and Smallbone from the bench, the latter making his first appearance in nine months after suffering a serious knee injury at the start of the year.
The Academy graduate’s first touch had all the makings of a fairy-tale return when Long’s cross deflected kindly into his path, but the 21-year-old’s header was too close to Kepa, who clearly had not read the script.
Hasenhüttl played his final card with penalties looming by bringing on Chelsea old boy Tino Livramento for the weary Djenepo, but Smallbone skewed a half-chance wide and Callum Hudson-Odoi fired into the side-netting as the 90 minutes ticked over into stoppage time.
Saints kept pushing, forcing a dramatic sequence of corners from which Kepa kept his team in it, tipping one header over from the impressive Lyanco, before beating out another from Salisu as Chelsea held on for spot-kicks.
Adam Armstrong stepped up first for Saints and scored emphatically, but Walcott was denied by penalty specialist Kepa.
Saints have an imposing presence of their own between the sticks in Forster, who saved superbly from Mount, but Marcos Alonso, Hudson-Odoi and Chilwell all scored.
Long and Romeu found the net to keep the visitors in it, but it was Saints’ fourth penalty, skied by Smallbone, that allowed James to win the shoot-out for the hosts.