Okubo started on the right flank of Alberto Zaccheroni's preferred 4-2-3-1 formation in Monday's friendly and was replaced by regular starter Shinji Okazaki at the break.
Japan struggled to produce the ideal final pass or shot in the first 45 minutes with Okubo and Yuya Osako on the pitch but the introduction of Okazaki and Yoichiro Kakitani in the second half saw Zaccheroni's men triumph 3-1.
But despite having never played as a right winger before, Okubo argued he can be relied upon at Brazil 2014, if Zaccheroni wants to make changes.
"Since I didn't have any training for playing on the right wing, I had some worries when I was told I was starting as a right-winger," the 31-year-old told the Japan Football Association's website.
"But after the match I feel I did alright."
Okubo was the J. League's top scorer in 2013 with 26 goals for Kawasaki Frontale and notched another eight this campaign before the mid-season break for the World Cup.
But the former Vissel Kobe centre forward, who spent two seasons with Mallorca from 2004-06, has a poor international striking record with just five goals from 56 matches.
Okubo has not scored for Japan since 2008, underlining the problems the Asian side have had in finding a genuine centre forward over the past decade.
Midfielders Yasuhito Endo and Shinji Kagawa scored for Japan against Costa Rica, as did substitute forward Kakitani.
