Spain-based forward Takefusa Kubo said Japan "need to keep improving" after thrashing El Salvador 6-0 in a friendly Thursday to pick up their first win since the World Cup.
Kubo has been in impressive form for Real Sociedad this season, helping the Basque side finish fourth in Spain to qualify for the Champions League.
The 22-year-old was again to the fore as Japan made short work of El Salvador in Toyota, scoring one goal and setting up two others for the Blue Samurai.
Japan are aiming to win a record fifth Asian Cup title in Qatar in January and Kubo urged his team-mates to keep building momentum when they play Peru in a friendly in Osaka on Tuesday.
"This is the level that we're at at the moment, and we need to keep improving," said Kubo, who swept home a pass from Brighton winger Kaoru Mitoma in the first half.
"Our next opponents will be stronger so we need to go again and get ready for the next game."
Japan scored twice in the first four minutes against El Salvador, which had defender Ronald Rodriguez sent off with two minutes on the clock.
Shogo Taniguchi headed home a Kubo free-kick in the first minute, before Ayase Ueda picked himself up after being fouled by Rodriguez to add a second from the penalty spot.
"It was down to our positivity that we made a good start," said Japan coach Hajime Moriyasu.
"That also made things difficult but the players had to work out what to do and that makes us a better team."
Kubo scored Japan's third midway through the first half, before Ritsu Doan tapped in shortly before the break.
Substitutes Keito Nakamura and Kyogo Furuhashi added two more goals in the second half.
Celtic striker Furuhashi was making his first international appearance in nine months, after being passed over for Japan's World Cup squad.
The 28-year-old, who was named Scotland's player of the year after scoring 27 goals for champions Celtic this season, leaped above the El Salvador defence to score with a header.
Japan claimed their first win since losing to Croatia in the last 16 at the World Cup, following a draw against Uruguay and a defeat to Colombia in March friendlies.
"The players won't always be in the starting line-up -- they can also come off the bench and give us energy," said Moriyasu.
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