The visitors opened the scoing with a penalty courtesy of fly-half Ronan O'Gara but their hopes were dealt a blow on the quarter hour when lock Paul O'Connell limped off the field to be replaced by Donnacha O'Callaghan.
Things got worse for the visitors when Williams cut through their defence for his opening five-pointer evading a series of desperates tackles for a superb score that was converted by Henson.
Munster rallied as the half come to a close with their forwards forcing a succession of penalties from the home side's pack that eventually led to a yellow card for Duncan Jones and a penalty try.
But they failed to maintain that level of pressure after the break and ten minutes into the second period Andrew Bishop created the space for Williams to notch his second that was again converted by Henson.
Spice rounded out the scoring with the game's final try on the hour although they came close to securing the bonus point in injury time.
|Ospreys Score Card|
|Munster Rugby Score Card|