Japan slumped to a shock 1-0 defeat against Oman in the opening game of the 2022 World Cup final Asian qualifying round on Thursday.
Issam Al Sabhi scored the 88th-minute winner four minutes after coming off the bench as Hajime Moriyasu's men remained disjointed and second-best throughout the Group B game at a rainy Panasonic Stadium in Suita.
Japan, currently 24th in the FIFA rankings, have reached the last six World Cup finals since their debut in 1998.
"They dominated the game, they've prepared well. It was a difficult game," said Moriyasu. "It turned out to be a really frustrating defeat. We'll make our best preparation to get three points in the next game."
Japan were without the new Arsenal signing Takehiro Tomiyasu as he completed the transfer and Liverpool's Takumi Minamino remained on the bench following a left thigh complaint.
But Samurai Blue looked sluggish regardless after the majority of the players flew back from Europe, getting played off the park by the 79th-ranked opponents who have had a monthlong training camp to prepare for the game.
"It wasn't good at all. We need to raise our intensity more than anything, with no holding back," said captain Maya Yoshida.
Japan, who brought on the on-form Kyogo Furuhashi to replace an anonymous Genki Haraguchi in the left attacking midfield at halftime, had Ito's header saved and Wataru Endo's close-range effort deflected before they survived a penalty scare in the 51st minute.
Abdullah Fawaz beat Hiroki Sakai down the left and sent in a cross that took a touch before hitting the left arm of Yuto Nagatomo. The referee pointed to the spot but overturned the decision after a VAR check when the arm was judged to not have been outstretched from the body.
Oman continued to push, Ali Al-busaidi this time beating Sakai only to see his powerful effort denied by the head of keeper Shuichi Gonda from a tight angle on the hour mark.
Osako's low drive from the edge of the box forced a diving save from Al-rushadi five minutes later as Japan introduced Ritsu Doan and Takefusa Kubo to provide spark to the attack, but Salah Al-yahyai, who has been a danger throughout, deservedly set up the winner.
Good combination play breached the left side of the Japanese defense before Al-yahyai's cross was met on a volley by Al Sabhi, with the ball bouncing into the far corner.
"They sat back and we couldn't break them down from the first half," said veteran Nagatomo. "We couldn't adjust in the second half either and it was a defeat that shouldn't have happened."
The defeat means Japan's head-to-head record against 79th-ranked Oman fell to 9-1 with three draws.
Japan will face China on Tuesday, with the away game moved to a neutral venue in Doha due to COVID-19 travel restrictions.
Saudi Arabia, Australia and Vietnam are also in the same group with top two teams after a six-team round-robin earning automatic qualifications for the World Cup in Qatar.