Substitute Arturo Lupoli scored a late winner to earn Arsenal a 1-0 victory over hosts Ajax on the first day of the Amsterdam four-team tournament on Friday.
Earlier, Porto defeated Argentina's Boca Juniors 2-0 in the opening match.
Arsenal controlled their game and broke through with three minutes to go when Italian Lupoli, who played most of his soccer in the youth and reserve teams late season, netted from the edge of the penalty area after good work by new signing Alexander Hleb.
"It was a difficult match because we played with a closed roof and that is something I really don't like," Arsenal manager Arsene Wenger told reporters.
"We played well against a defensively well-organised team that aimed to play on the break.
"Finally we scored a late goal after missing easier chances earlier in the match."
Ajax coach Danny Blind was not surprised that Arsenal dominated.
"It was interesting to see how we did against a good team," said Blind.
DEFLECTED SHOT
"It taught me a lot about how my team handles these situations and it was logical that Arsenal pushed us back in defence."
Porto, the 2004 European Cup winners, opened the scoring against Boca when a deflected shot by Helder Postiga beat goalkeeper Roberto Abbondanzieri in the 19th minute.
The Portuguese team, coached by former Ajax boss Co Adriaanse, were on top throughout and sealed their win in the 73rd minute.
New signing Fatih Sonkaya broke through on the right and his cross gave Hugo Almeida the opportunity to set up Brazilian Jorginho for the second goal.
"The circumstances were difficult and my team is physically not 100 percent but our performance satisfied me," said Adriaanse.
"My defence were well organised and in offence I had intelligent players like [Benni] McCarthy and Postiga who can make the difference.
"We are still preparing for the season but we came here to win this tournament."
The players rest on Saturday before the competition ends the following day when Porto take on Arsenal and Ajax face Boca.
Teams get three points for a win, one point for a draw and a point for every goal scored.