如何使用爆炸在每三个空间之后拆分？

I have a string as given below:

$str = "In order to successfully build your backlinks in a highly competitive industry (or if you're targeting highly competitive keywords), you have to get smart about your strategy. That means using the best back-link building tools available";

Now I want to split the string after every third word. That is I want..

split1 = in order to
split2 = successfully build your
split4 = backlinks in a

and so on till the end of the string.

I have already done it using preg_match_all but it isn't giving me what I want. So can someone help me out with it to split the string using the split() or preg_split or the explode() function.

Thank you

$split = explode(' ', $str); // Split up the whole string
$chunks = array_chunk($split, 3); // Make groups of 3 words
$result = array_map(function($chunk) { return implode(' ', $chunk); }, $chunks); // Put each group back together

DEMO

$result is:

Array
(
    [0] => In order to
    [1] => successfully build your
    [2] => backlinks in a
    [3] => highly competitive industry
    [4] => (or if you're
    [5] => targeting highly competitive
    [6] => keywords), you have
    [7] => to get smart
    [8] => about your strategy.
    [9] => That means using
    [10] => the best back-link
    [11] => building tools available
)