<?php

$A1 = Array
(
    "0" => Array
    (
        "match" => "1",
        "when" => "2013-10-13 15:00:00",
        "a" => "AD",
        "b" => "NiP",
        "winner" => "c",
        "closed" => "1",
        "event" => "Fragbite Masters",
        "format" => "3",
    ),
    "1" => Array
    (
        "match" => "2",
        "when" => "2013-10-13 15:00:00",
        "a" => "VG",
        "b" => "AD",
        "winner" => "a",
        "closed" => "1",
        "event" => "Starseries",
        "format" => "5",
    )
);

$A2 = Array
(
    "0" => Array
    (
        "match" => "1",
        "a" => "58",
        "b" => "107"
    ),
    "1" => Array
    (
        "match" => "2",
        "a" => "174",
        "b" => "162"
    )
);

function key_compare_func($arr1, $arr2)
{
    $newarray = array();
    $match = "match";
    $whereKey1 = "a";
    $whereKey2 = "b";
    $newKey1 = "per_a";
    $newKey2 = "per_b";

    if(is_array($arr1) && is_array($arr2)){
        if($arr1[$match] == $arr2[$match] ){
            $newarray = array_merge($arr1, array($newKey1 => $arr2[$whereKey1], $newKey2 => $arr2[$whereKey2]));
        }
    }
  return $newarray;
}

$modifiedArray = array_map("key_compare_func",$A1, $A2);
echo '<pre>';print_r($modifiedArray);echo '</pre>';