Japan produced a stunning comeback to shock Germany in their World Cup opener on November 23 after the four-time champions staged a powerful protest against FIFA's refusal to allow rainbow-themed armbands, while Spain started in style by putting seven past Costa Rica.
Elsewhere on the fourth day of action in Qatar, Belgium edged out Canada 1-0 while 2018 finalists Croatia drew with Morocco.
The build-up to the Group E match between Germany and Japan in Doha was dominated by intense speculation over whether German captain Manuel Neuer would wear the "OneLove" armband, viewed as a symbolic protest against laws in the Gulf state, where homosexuality is illegal.
Seven nations, including England and Germany, had abandoned plans to wear the armbands because of the threat of disciplinary action from world governing body FIFA.
Bayern Munich goalkeeper Neuer, who had come under political pressure to change his mind, did not wear the armband at the Khalifa International Stadium. Instead, the entire team covered their mouths before kick-off.
"It wasn't about making a political statement – human rights are non-negotiable," Germany's football federation tweeted minutes later.
Watching in the stadium, German Interior Minister Nancy Faeser did wear the armband while Qataris around her wore armbands bearing the keffiyeh headdress in a show of support for the Palestinian cause.
Germany came to the World Cup desperate to avoid the humiliation of 2018, when as defending champions they suffered their earliest exit since 1938.
Hansi Flick's men were on course for an opening win when Ilkay Gundogan put them ahead from the penalty spot in the 33rd minute.
However, they then paid the price for missed chances as the Blue Samurai equalised through Ritsu Doan in the 75th minute.
Fellow substitute Takuma Asano – who, like Doan, plays in the Bundesliga – completed a remarkable turnaround eight minutes later, smashing the ball home to give Japan a famous 2-1 victory.
"The players came together as one team, we prepared well and we stuck in there, and that's what led to the win," said Japan coach Hajime Moriyasu.
Germany are once again facing the prospect of World Cup humiliation, with Spain to come next.
Bayern forward Thomas Mueller told Germany's Magenta TV it was "ludicrous that we are now standing here with a defeat".
Costa Rica crushed
Spain's start in Qatar was in stark contrast to that of Germany as Luis Enrique's side crushed Costa Rica 7-0 at Al Thumama Stadium to claim their biggest ever win at the World Cup.
Dani Olmo and Marco Asensio both scored before two Ferran Torres goals either side of half-time, the first of which was a penalty.
Eighteen-year-old Gavi got their fifth goal, becoming the youngest goalscorer at a World Cup since Pele aged 17 in 1958.
Substitutes Carlos Soler and Alvaro Morata then put the seal on an emphatic victory for the 2010 world champions.
Luis Enrique said afterwards that his players were "superb" before adding: "We still have room to improve".
Belgium win, Croatia held
Wednesday's late game saw Belgium take on a Canada side who are back at the World Cup for the first time in 36 years.
Time is running out for Belgium's so-called "Golden Generation", who finished third at the last World Cup.
They could have fallen behind in the Group F encounter but goalkeeper Thibaut Courtois came to the rescue by saving an early Alphonso Davies penalty.
Starting in the absence of Romelu Lukaku, Michy Batshuayi then scored the only goal of the game for Roberto Martinez's side.
Earlier Luka Modric and Croatia were frustrated by Morocco in a 0-0 draw in the same section.
Brazil begin their campaign in the early hours of November 24 (2am Cambodian time) with the record five-time winners playing Serbia.
Cristiano Ronaldo's Portugal face Ghana, two days after he left Manchester United by "mutual agreement" after a bombshell interview last week in which he lashed out at the club.
South Korea coach Paulo Bento confirmed that Tottenham Hotspur forward Son Heung-min was fit enough to play against Uruguay even though he has been training in a face mask.
But he cautioned that they "cannot take any risks" with the player, who suffered a fracture around his left eye earlier this month.
England goalkeeper Jordan Pickford said Harry Kane was "fine", easing fears the captain could miss Friday's Group B clash against the USA.
Kane went for a scan on Wednesday after he hurt his right ankle in England's 6-2 win over Iran.