The first half was relatively sparse in action, with few clear-cut chances being created by either side throughout the first 45 minutes of what would end up being a close game.
The aforementioned Spanish midfielder had, at least in the first half, a more comfortable outing in a Chelsea shirt than he had done in his previous starts, which Blues' fans will hope is a more promising sign of things to come.
Just before the interval though, the home side did go ahead courtesy of another header, this time from Kai Havertz, and his effort looped over and ended up in the bottom right corner.
Chelsea FC (@ChelseaFC) October 26, 2021
It was not two minutes after the game had restarted however than when Southampton got an equaliser through Che Adams, who had the simplest of tasks when the ball fell to him just a yard out after Kepa Arrizabalaga couldn't hold onto a Kyle Walker-Peters shot.
Thomas Tuchel's backup keeper didn't let that one error affect him though, and he went on to have an excellent rest of the game, including making two brilliant saves in injury time.
Both of them came from headers as a result of a whole host of corners, bombarding the Chelsea penalty area, but the 27-year-old was equal to them, sending the game to a penalty shootout.
He again excelled during the spot kicks, saving from Theo Walcott before William Smallbone fired over the bar, giving Reece James the chance to win it for Chelsea.
Kepa in his element. 💪 pic.twitter.com/J4QMYcrmxh— Chelsea FC (@ChelseaFC) October 27, 2021
Kepa the shootout hero again
That reputation, gained after refusing to be substituted by Maurizio Sarri in the final of this competition prior to a penalty shootout against Manchester City, was one that many thought would be permanently attached to him at Stamford Bridge.
To his enormous credit however, he has revitalised himself and, despite no longer being the first choice goalkeeper, has conducted himself with admirable professionalism and stepped up when asked.
The Spanish international has only played four games this season, with three of them resulting in penalty shootouts (all of which the Blues have won), which stands him in good stead for any further spot kicks to be faced in cup competitions later in the campaign.
Not only that, but even when Mendy is called away, as expected, to international duty with Senegal in January due to AFCON, he will be able to slot straight into the team, with worries over his form no longer present in either his mind or those of the fans.
That's because it's not only penalties that Kepa has shown himself to be adept at - the two world-class saves he pulled out of the bag in additional time at the end of the second half prevented his side from an embarrassing defeat at home - what would've been their first of the season.
Carabao Cup (@Carabao_Cup) October 26, 2021
Instead, as it turned out, he gave Tuchel's team the opportunity to put things right and, more importantly, to show once again why he is as good a backup as a manager could ask for.
Attacking options remain limited
While all the headlines will rightfully be about the penalty heroics of Kepa, had the Blues not come out on top there would've been more focus on the lack of clinicality against Southampton.
Of course, it's important to caveat this with the fact that it was evidently a second-string side on the field, but with the supposed individual quality of such players, questions ought to be asked.
It was the former who was noticeably absent from any of the home side's attacks, as the Moroccan winger appeared unwilling to put much, if any, effort in whatsoever.
Not only that, but when chances did fall to the feet of players in blue shirts, there were multiple wasted opportunities in which the game could, and should have been put to bed.
It's perhaps harsh to criticise Saul Niguez for wastefulness - after all, he is predominantly a defensive midfielder - but he had an excellent chance to put Chelsea ahead, but fired a shot low and wide of the post from the edge of the box.
The gaffer's assessment on last night's victory. 👇— Chelsea FC (@ChelseaFC) October 27, 2021
Overall, while it was by no means a terrible performance, it was not one that Thomas Tuchel will reflect on particularly fondly, particularly given quite how careless his side were when they did manage to carve out a rare chance.
Nevertheless, in the early rounds of any cup competition, the main thing for a team like Chelsea is simply to progress and, while they might have made it harder for themselves than they would have liked, they did so eventually, and as is often said - that's the sign of potential champions.