Mexico 1 - 0 Germany
Germany were stunned 1-0 by Mexico in the opening game of their World Cup defence on Sunday as Hirving Lozano finished off a sharp counter-attack that exposed the ragged defending that the four-times winners had displayed in their warm-up games.
Germany's defence had looked stretched to breaking point on several occasions in the opening half-hour, and it was no surprise when Javier Hernandez again left Mats Hummels for dead to play in Lozano, who cut inside Mesut Ozil and smashed the ball low into the corner to release an explosion of noise in Luzhniki Stadium.
Germany came close to levelling late in the half when a Toni Kroos free kick was touched on to the bar by goalkeeper Guillermo Ochoa, and they gradually took command once Marco Reus joined the fray after an hour and introduced some pace to their attack.
But despite almost constant pressure they were largely kept at long range, and their poor finishing rarely threatened Ochoa as Mexico held out for only their second victory against the Germans in 12 attempts.
Brazil 1 - 1 Switzerland
A second-half header from Steven Zuber cancelled out a sensational early goal from Philippe Coutinho as Switzerland and Brazil drew 1-1 in a tight Group E World Cup opener.
With 20 minutes gone, Coutinho gathered a clearance 25 yards from goal and curled a marvellous shot into the far corner off the post to give the five-times world champions the lead.
However, Switzerland, who had looked toothless throughout the first half, got back on level terms five minutes into the second period when Zuber rose unmarked to head home a corner kick. Coutinho had Brazil's best chance after the break but shot wide.
Serbia 1 - 0 Costa Rica
Aleksandar Kolarov produced a moment of captain's inspiration, curling home a superb free kick as Serbia got their World Cup Group E campaign up and running with a 1-0 victory over Costa Rica on Sunday.
With the Central Americans proving a tough nut to crack, Kolarov stepped up to bury a 25-metre effort from wide on the right, lighting up an otherwise tight game in the southern Russian city of Samara.
Serbia had dominated against a Costa Rica side who rarely threatened after a bright start, but chances were thin on the ground until Kolarov made the breakthrough in the 56th minute.
With Brazil heavy favourites to win the group, which also features Switzerland, the victory delivered a potentially vital three points for Serbia and lifted a weight from coach Mladen Krstajic, in what was his first competitive game.
"Frankly speaking, there was a great deal of pressure on the team, and on me, over the past seven months," said the Serbia coach, who took the job in October.
Krstajic's relief was matched in equal measure by the disappointment of Costa Rica boss Oscar Ramirez, whose side are in a precarious position.
"Maybe we have lost a certain margin for qualifying," he said. "It's going to be difficult, but our intention remains the same. I told the lads in the changing room 'This isn't over'."
If Costa Rica are going to recover, however, they will need to rediscover the defensive organisation and clinical counter-attacks that propelled them to the quarter-finals four years ago.
While a number of their players remain the same from Brazil, they lacked the energy of that side.
Serbia found it hard to break them down, but they rarely looked troubled at the back and barring a late half chance for substitute Joel Campbell, they coasted through the game.
It had not looked like that in the opening minutes.
What to expect on day five
Day five of competition will see three matches back-to-back including Sweden playing South Korea, Belgium playing Panama, and England taking on Tunisia.
Chelsea playmaker Eden Hazard is in the best form of his life but Belgium need all their top players to be better than ever if they are to have any chance of winning the World Cup, goalkeeper Thibaut Courtois said on Sunday.
The Belgians are considered a good outside bet to lift the World Cup for the first time and start the tournament on Monday against rank outsiders Panama in Group G.
England will go into their opening game against Tunisia free of the psychological burden that has built up after a string of limp tournament exits, manager Gareth Southgate said.
England fell at the first hurdle in Brazil four years ago after failing to win a group stage game.
Two years later they were knocked out of Euro 2016 by tiny Iceland, leading to criticism that a team that was once one of the world's top sides had lost the mental strength to compete.
"I think the history will help us in terms of understanding what we can improve upon and what we can do. We learn lessons of the past," Southgate told reporters.
"This team shouldn't be burdened with it because they're a fresh group," the coach, who has promoted young players since his appointment in 2016, said. "The players of the past and the opportunities of the past are gone."
England go into Monday's Group G game in the Volgograd Arena against Tunisia tipped to advance to the next stage along with the Belgium. World Cup new boys Panama make up the group.