Get N top scores from a flat array and allow unlimited elements per qualifying score in the event of ties

I'm working on a leader board that pulls the top scorers into first, second, and third place based on points. Right now I'm working with a sorted array that looks like this (but could be of infinite length with infinite point values):

$scores = Array
    (
        ["bob"] => 20
        ["Jane"] => 20
        ["Jill"] => 15
        ["John"] => 10
        ["Jacob"] => 5
    )

I imagine I could use a simple slice or chunk, but I'd like to allow for ties, and ignore any points that don't fit into the top three places, like so:

$first = Array
    (
        ["bob"] => 20
        ["Jane"] => 20
    )

$second = Array
    (
        ["Jill"] => 15
    )

$third = Array
    (
        ["John"] => 10
    )

  $arr = array(
      "Jacob" => 5,
      "bob" => 20,
      "Jane" => 20,
      "Jill" => 15,
      "John" => 10,
  );
  arsort($arr);
  $output = array();
  foreach($arr as $name=>$score)
  {
      $output[$score][$name] = $score;
      if (count($output)>3) 
      {
          array_pop($output); 
          break;
      }
  }
  $output = array_values($output); 
  var_dump($output);

$first will be in $output[0], $second in $output[1] and so on.. Code is limited to 3 first places.

ps: updated to deal with tie on the third place