Arsenal were expected to give Sydney FC a massive test, but few could have predicted how they'd open the scoring on their Australian tour.
It didn't take long for the Gunners to get their trip Down Under up and running but it was an unlikely source that fired them into a fourth minute lead against the A-League champions at ANZ Stadium.
Some slick work from Arsenal debutants Joe Willock and Reiss Nelson saw the visitors win a corner, which the ever-reliable Mesut Ozil whipped into the danger area.
Sydney tried to head the ball awy from their own goal box but the attempted clearance fell invitingly to Per Mertesacker.
The giant Gunners' captain showed instincts more familiar with Arsenal superstar Alexis Sanchez as he swivelled on the spot and flicked the ball into the bottom corner of goal.
Arsenal record signing Alexandre Lacazette started off the bench for the visitors, having joined the club last week from Lyon for PS46.5million ($A79 million)
As well as Sydney FC, the Gunners will play Western Sydney Wanderers at Sydney's ANZ Stadium on Saturday night.