Atletico Madrid goalkeeper Antonio Adan saved three penalties and scored the winning kick as Arsenal lost their International Champions Cup match.
The 31-year-old, who was a half-time substitute, had a remarkable debut in Singapore after signing from Betis.
Arsenal teenager Emile Smith-Rowe cancelled out Luciano Vietto's opener to take the game to a shootout.
But Henrikh Mkhitaryan, Joseph Willock and Edward Nketiah were all denied by Adan as Atleti won 3-1 on penalties.
Arsenal were on top for most of the game as their Spanish opponents were without the likes of Antoine Griezmann, Diego Godin and Diego Costa.
Arsenal boss Unai Emery gave action to new signings Bernd Leno, Sokratis Papastathopoulos and Matteo Guendouzi but it was 17-year-old Smith-Rowe who took his chance with a fine individual goal.
Atleti's first-choice keeper Jan Oblak made three excellent first-half saves but they took the lead against the run of play when Vietto headed in a fine cross, giving new £19m keeper Leno no chance.
Smith-Rowe, who along with fellow teenagers Reiss Nelson and Guendouzi impressed throughout, then levelled with a brilliant goal, slaloming in from the left, beating two defenders and then curling past Adan.
Emery made eight changes after an hour as new centre-back Papastathopoulos got a run-out in a change of system.
The game petered out and went straight to a shootout, with Ainsley Maitland-Niles scoring from the spot for Arsenal, while Rodri, Victor Mollejo and Adan were successful for Atletico.
The Gunners play Emery's former club Paris St-Germain in the same stadium on Saturday afternoon, while Atleti face the French side two days later.
Emery 'confident' Ramsey will stay
Arsenal manager Unai Emery on midfielder Aaron Ramsey - who has less than 12 months left on his deal:
"Aaron is a very important player for us and I want him to stay and work with Arsenal, to show his quality, and I am confident he will stay.
"This was the stage for a young player like Smith-Rowe to show the quality that they possess. Arsenal will always give young players a chance to work with us, to show their qualities in each match."
Atletico: Oblak, Juanfran, Moya, Montero, Olabe, Rodrigo, Joaquin, Partey, Correa, Gameiro, Vietto.
Arsenal: Leno, Bellerin, Holding, Mustafi, Kolasinac, Nelson, Ramsey, Guendouzi, Smith-Rowe, Aubameyang, Lacazette.