Chelsea had started the first haft brightly and went ahead through Hakim Ziyech to lead 1-0 at the interval, though their joy was tempered by a worrying shoulder injury for the winger.
That injury seemed to take the wind out of Chelsea’s sails for the second half, and Gerard Moreno deservedly levelled the score 1-1 after the break to take the game to extra-time and a penalty shootout.
The extra time ended 1-1 at Belfast’s Windsor Park ground, with Chelsea replacing goalkeeper Edouard Mendy with Kepa in the final seconds in what turned out to be a master-stroke as penalties loomed.
Kai Havertz missed the first spot-kick but after that Chelsea were perfect while both Aissa Mandi and Raul Albiol both saw their penalties saved by Kepa as Chelsea won 6-5.
How Chelsea Won UEFA Super Cup
When Havertz saw the first kick saved by Asenjo, Kepa was already under pressure and though he was unable to keep out Gerard Moreno’s kick, he did save well from Aissa Mandi.
Cesar Azpilicueta, Marcos Alonso and Mason Mount all converted their penalties before Jorginho also beat Asenjo, putting right his error from the spot in the final of Euro 2020 just weeks earlier.
It went to the seventh kicks with Antonio Rudiger stroking the ball calmly home before the veteran Albiol was unable to match him, Kepa saving smartly away to his right.
The decision to bring Mendy off for Kepa raised eyebrows, but he eventually came up trumps to help the Blues win the Super Cup for the second time – their first coming in 1998 when they beat Real Madrid.
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The victory gives Thomas Tuchel his second trophy as Chelsea manager following their Champions League triumph at the end of last season in May.