Williams hadn't scored for his country on home turf for almost a year but the 32-year-old produced two typically opportunistic scores to help Wales to a convincing win.
The current IRB World Player of the Year pounced on a charged down box kick just seconds after half-time, before claiming Wales' third and final try with an incisive run with 15 minutes left in Cardiff.
The brace of scores took Williams' international tally to 50, with 48 coming in Welsh colours and a further two for the British & Irish Lions against South Africa four months ago.
Wales coach Warren Gatland selected 21 Magners League players in his matchday 22 and 14 in his starting line up and his team produced a more comprehensive performance than they had done in edging to victory over Samoa eight days ago.
Scarlets fly-half Stephen Jones set the Welsh on their way against a Pumas side who ran England close at Twickenham last weekend.
Quick thinking from the veteran playmaker resulted in the first try of the match as Jones caught the Argentine defence napping by taking a quick tap penalty and sprinting 20 metres to the line with 17 minutes played.
Jones converted all three Welsh tries and added two penalties, with Blues wing Leigh Halfpenny also contributing six points courtesy of two long-range penalties of his own.
Martin Rodriguez was Argentina's sole scorer - the inside centre kicking three penalties and converting his own 60th-minute score after debut starter Jonathan Davies misplaced an attempted kick ahead inside Welsh territory.
Wales now prepare to face Australia in a week's time, hoping to make it three wins from four in their quartet of autumn internationals.
Wales: James Hook (Ospreys), Leigh Halfpenny, Jamie Roberts (both Blues), Jonathan Davies (Scarlets), Shane Williams (Ospreys), Stephen Jones (Scarlets), Gareth Cooper; Gethin Jenkins (both Blues), Matthew Rees (Scarlets), Paul James, Alun-Wyn Jones (both Ospreys), Luke Charteris (Dragons), Andy Powell, Martyn Williams (both Blues), Ryan Jones (Ospreys, captain)
Replacements: Duncan Jones (Ospreys) for Paul James (57); Dwayne Peel (Sale Sharks) for Gareth Cooper (66); Huw Bennett (Ospreys) for Matthew Rees (68); Jonathan Thomas (Ospreys) for Luke Charteris (68); Andrew Bishop (Ospreys) for Jonathan Davies (73); Tom James (Blues) for Shane Williams (73), Dan Lydiate (Dragons) for Andy Powell (73)
Guinness PRO12
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