Erik Lamela's second-half goal lifted Argentina to a 1-0 victory over Mexico in Group F.
Lamela, who is headed to Italian club Roma from River Plate, broke from midfield in the 71st minute and blasted a 20-meter (yard) shot inside the far post, beyond Mexico goalkeeper Carlos Lopez.
Brazil took the lead by in their Group E opener but Egypt equalized and spurned good opportunities to take a surprise win.
Argentina's victory will be welcome in a proud football country that has been having problems. The senior national team was ousted from the Copa America in the quarterfinals, prompting the firing of coach Sergio Batista.
Under-20 coach Walter Perazzo has acknowledged his job may also be on the line if Argentina does not make the semifinals.
Argentina has won five of the past eight U20 World Cups, and six overall - the most by any nation.
''Mexico at times controlled the ball,'' Perazzo said. ''But whenever we had it we generated the most dangerous chances.''
''This gives the group confidence,'' he said. ''Winning the first game is very important.''
Mexico seemed to have scored in the 48th minute when Alan Pulido chipped the ball past keeper Esteban Andrada, but the play was correctly ruled offside.
''We planned to attack in the match,'' Mexico coach Juan Carlos Chavez said. ''We are a team that can score, but today it didn't happen.''
Brazil was lucky to get the draw against Egypt. Danilo gave Brazil a 1-0 lead in the 12th minute with a header from a corner, but Egypt equalized through Omar Gaber in the 26th and was a bit unlucky not to take all three points.
Gaber could have given Egypt at 2-1 lead in the 48th, but despite taking his time and being left along he shot just wide of the far post from 12 meters (yards).
In the 85th, Egypt goalkeeper Ahmed Elshenawi had to leave the match after being struck in the face by Henrique, who chased a loose ball into the area and inadvertently kicked Elshenawi in the face. Egypt had a substitution up its sleeve to allow the back-up keeper to come on.
The performance has to make Egypt one of the early dark-horse choices for the title while casting doubt on the claims of Brazil, which is a perennial favorite in any tournament.
England had the better chances but could not break through against the under-19 Asian champions North Korea.
''We were the better team in the first 45 minutes,'' England coach Brian Eastick said. ''For a team that was only put together two weeks ago, their performance was very good. Our players in that dressing room are very disappointed we didn't win this game today.''
England is not able to field its best players who have remained at home to prepare for the upcoming season. More than 30 players were withheld by their clubs for preseason training.
Eastick said he understands the problem of scheduling the tournament, which would never suit every country. But he did question the clubs for withholding players, most of whom are not first-team players.
''The players who are not here are missing a fantastic opportunity,'' Eastick said.
Panama goalkeeper Luis Mejia made a handful of difficult saves to salvage the draw and keep the Central Americans in the match with Austria. His best save came in the 54th when he pulled off an impressive block on a Daniel Offenbacher shot.
Stephen Wade can be reached at http://twitter.com/StephenWadeAP