The landmark strike at the Millennium Stadium puts Williams ahead of All Blacks great Doug Howlett and into joint-third place alongside former England flying wing Rory Underwood on the all-time try-scoring list.
But deadly wing wizard Williams, who has struck 48 times for Wales and twice for the British Lions, insists there is plenty more to come.
Williams, 32, said: "It's a great honour and I'm really pleased to score 50 tries.
"It will be great to tell the children and grandchildren when I hang the boots up but I am just as happy when I scored my first try for Wales.
"The accolade of scoring the number of tries is just a bonus to me and I won't let the feat affect me. I never expected it would happen and it still feels mad. I don't want to get carried away because I feel there is more tries in me.
"Hopefully I get picked to face Australia next weekend and if I score to become the greatest in the northern hemisphere, then I'll be a happy man."
Only Japan's Daisuke Ohata with 69 tries and Australian legend David Campese stand in the way of Williams becoming the greatest finisher of all-time.
And the Ospreys ace admits he has Campese, on 64 touchdowns, in his sights ahead of the mouth-watering clash with the Wallabies next Saturday.
Williams added: "When you look back in history to the likes of Campese, it's a massive honour for me to be mentioned alongside quality players like him.
"I'm still enjoying my rugby and believe I'm capable of scoring even more - it's my job.
"I want to get up to David Campese one day and I hope number 50 wasn't the last of my tries. I want people to be talking about my 51st and 52nd tries and so on."
Fly-half Stephen Jones set Warren Gatland's men on their way with an opportunist first-half touchdown in a 17-point haul while Argentina centre Martin Rodriguez scored all the visitors' points as Wales eased home.