Arsene Wenger admits he did not know why Alexis Sanchez, rather than regular spot-kick expert Santi Cazorla, took a penalty that was saved in the 4-1 win over Hull City.
Sanchez had already put his name on the scoresheet and later added Arsenal's third goal on Saturday, but Hull goalkeeper Eldin Jakupovic saved his effort from 12 yards and Wenger confirmed Cazorla was above the Chilean striker in the club's list of penalty takers.
Further goals from Theo Walcott and Granit Xhaka ensured Arsenal came away from the KCOM Stadium with an emphatic result and their third consecutive Premier League victory, and Wenger praised the fluency of their performance.
As for the penalty, Wenger told BBC Sport: "Santi was down to take it. I don't know why it did not happen; we have [a] pecking order, it was not planned for Sanchez to take it.
"I want to know what happened and for it not to happen again. Overall anyone can miss a penalty, we have to accept that. It has happened to all of us and it has happened to Santi Cazorla as well.
"Overall it was a positive performance after having played away in the Champions League.
"We started well, we were quite dominant, our game was fluent. They defended very well and tried to catch us on the break but overall we managed to score the goal after we missed a penalty.
"After that it was 11 against 10 and down to us to be serious and not concede any goals."
Arsenal's 20-year-old Nigerian winger Alex Iwobi put in an eye-catching performance that earned him the praise of his manager.
Wenger said: "It's only his second game since he came back from injury but today he had more presence in the game, more confidence when he takes the ball and he can be very dangerous going forward."
Pre-season signing Xhaka has struggled to break into the Arsenal side since joining from Borussia Monchengladbach, but Wenger was happy to see his long-range strike hit the net.
"I'm very happy for him," said the Frenchman. "When you come to a new club and there's a lot of competition going on you look for confidence and to show that you're a good player.
"To score goals helps with that confidence. He has that in him, he has it in the locker, shots from distance and left footed players usually have that."