The winner of Valentin Carboni in the second half of the stop time saw Inter from behind to beat the Urawa Reds 2-1 to pick up their first victory at the Club World Cup.
Match report
Lautaro Martinez had drawn the internal level in the 78th minute after Ryoma Watanabe had given the Japanese side, but Carboni was present to steal all three points.
The result lifts Cristian Chivu's side to the top spot in group E for the collision of River Plate with Monterrey, with the Argentinian giants then for the Nerazzurri.
Maciej Skorza's side came to the front early when the cutbacks of Takuro Kaneko found Watanabe, which stroked the ball home with the help of a matteo bowel.
Inter pulled almost seven minutes after he fell behind when Martinez rose the highest to meet the cross of Kristjan Asllani, but his efforts canons against the bar.
After not finding an equalizer before the break, the Serie A side began to turn the screw in the second half, with Asllani and Federico Dimarco who shot in the body early.
Inter continued to push and came closest in the 70th minute through replacement Henrikh Mkhiticyan, but their pressure eventually told 12 minutes of the time.
The inviting corner kick from Nicolo Barella became acrobatic in the back of the net by Inter Captain Martinez in the back of the net, and there would be a final turn to Lumen Field.
In the second minute of the second half of the stop time, Petar Sucic saw his effort blocking, but the ball was friendly to Carboni, who wiped the ball past Shusaku Nishikawa. Data debrief: Better late than never
Inter were made to work for their victory against the Urawa Reds, with their individual quality in the last third finally paid off when they came closer to the last 16.
But they had to find out from the early strike of Watanabe, the very first goal scored by an Asian team against an Italian side in the history of the club's World Cup.
And Martinez's fine finish set them up. The Argentin has now scored 10 goals in 10 games in the international competition in 2025 (Champions League and Club World Cup), although it was Barella who stole the show on Saturday.
The midfielder ended the match with team -high Totals for created opportunities (seven), passes in the last third (63) and successful dribbles (three), while also the joints for Inter (four, level with Asllani).
Match -Events
11 'goal! Inter 0-1 Urawa Red Diamonds (Ryoma Watanabe)
78 'goal! Inter 1-1 Urawa Red Diamonds (Lautaro Martínez)
92 'goal! Inter 2-1 Urawa Red Diamonds (Valentín Carboni)
Line-ups
Inter XI: Sommer, Darmian, De Vrij, Dimarco, Barella, Lautaro, Carlos Augusto, Esposito, Nicola Zalewski, Luis Henrique, Asllani
Subs: mkhitaryan, acerbi, di Gennaro, Bastoni, Josep Martínez, Petar Sučić, Alessandro Culigaris, Valentín Carboni, Francesco Pio Esposito, Tomás Palacios, Thomas Berbruch, Gabriele Cocchi, Gabriele, Gabriele, Gabriele, Gabriele, Gabriele, Gabriele, Gabriele, Gabriele, Gabriele, Gabrile, Gabriele, Gabriele, Gabriele, Giacchi, Gabrieli, Gabriele, Gabrile, Giacchii, Gabrieli, Giacchii, Gabrile, Giacchiii
Urawa Red Diamonds XI: Shusaku Nishikawa, Marius Høibråten, Gustafson, Ryoma Watanabe, Yoichi Naganuma, Matheus Savio, Hirokazu Ishihara, Danilo Boza, Takuro Kaneko, Yusuke Matsuo, Kaitouiz
Subs: Haraguchi, Thiago, Ayumi Niekawa, Shoya Nakajima, Takahiro Sekine, Taishi Matsumoto, Takuya Ogiwara, Rikito Inoue, Shun Yoshida, Tomoaki Okubo, Toshiki, Humpeir Komori, Kenta Nemoto