The Gunners, who also had Folarin Balogun in their team, thrashed the MLS trio of Christian Benteke, Jesus Ferreira and Denis Bouanga to go 1-0 up.
Taking aim from 12 yards out, each player had 60 seconds to score as many points as they could.
Targets placed around the goal ranged from two, five and ten points, with a moving target worth 20 points introduced with 20 seconds to go.
And it was Timber that top scored in the event with a whopping 50 points - just 15 points off the record that was set last year by Hector Herrera.
His fellow defender Kiwior meanwhile scored 49 points, as Arsenal beat MLS 121-88 to win the challenge.
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In contrast, Inter Milan target Balogun scored just 22 points - evidently leaving his shooting boots at home.
His low score meant that Arsenal would have won without Balogun in their three-man team.
Another striker that struggled was ex-Aston Villa, Liverpool and Crystal Palace star Benteke.
He mustered 27 points, with Arsenal easing to victory at the home of DC United.
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Arsenal and the MLS All-Stars are competing in the Skills Challenge a day prior to their clash on the football pitch.
The two teams, who faced each other in the MLS All-Star match, meet at Audi Field, where Timber and Declan Rice could make their Arsenal debut.