Extract a link in the_content()

You’re just looking in the wrong place:

php > $txt="<a href="http://tumblr.everlane.com/page/4">Everlane Tumblr</a>";
php > $matches = array();
php > echo preg_match_all('#\bhttps?://[^\s()<>]+(?:\([\w\d]+\)|([^[:punct:]\s]|/))#', $txt, $matches);
1
php > print_r($matches);
Array
(
    [0] => Array
        (
            [0] => http://tumblr.everlane.com/page/4
        )

    [1] => Array
        (
            [0] => 4
        )
)