Martinez was left to reflect on what might have been, with England midfielder Ross Barkley unable to convert from the edge of the box just before Arsenal went ahead from the spot.
"I felt the key moment of the game was going to the second goal and we had made it a real uncomfortable game for Arsenal," he said.
"We had a great chance and, in nine out of 10 situations like that, Ross Barkley will hit the target.
"I can see why the referee gave the penalty, although I don't agree with the decision completely, because there is contact but the ball is challenged by both of the players.
"After that, we gambled a bit and the final scoreline does not reflect what happened in the game."
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