Much of Wales' early play was disjointed and littered with errors, but they ruthlessly took their scoring chances and fly-half James Hook made another composed goal-kicking contribution.
Number eight Andy Powell pressed a late claim for inclusion in coach Warren Gatland's 30-man World Cup squad by scoring Wales' opening try just before half-time.
Lock Alun-Wyn Jones then followed suit 90 seconds later, giving Wales a healthy advantage that they never looked like losing, before wing George North touched down seven minutes from time.
Hook slotted two conversions and three penalties, while his opposite number Felipe Contepomi replied with a penalty double and conversion of substitute prop Martin Scelzo's late try.
Both sides though will need to find at least another gear before their World Cup openers against South Africa and England respectively.
Gatland will welcome back several of his big guns for that Springboks clash in Wellington on September 11 - the likes of Shane Williams, Mike Phillips and Sam Warburton - and they will head to New Zealand following a strong August showing.
They beat England and Argentina on home soil after outscoring England on tries during a narrow defeat at Twickenham, and there were mercifully no fresh injuries to trouble Gatland.
He has already lost Gavin Henson, Matthew Rees and Morgan Stoddart from his World Cup plans, while the likes of Gethin Jenkins, Ryan Jones, Stephen Jones and Rhys Priestland have been nursing various ailments.
But Wales appeared to emerge unscathed from a largely disappointing encounter, while Argentina offered little to suggest they will revisit the heights of their last World Cup campaign when they finished third after beating France twice.
Contepomi missed an early penalty for the Pumas, yet Argentina still established an impressive rhythm as Lee Byrne was forced into making a try-saving tackle and the Wales forwards encountered difficulty at the breakdown.
It was an impressive opening by Argentina, whose trademark forward power quickly surfaced to give Wales plenty of food for thought.
When Wales had possession they were guilty of forcing passes, and their high error-count merely played into Argentina's hands.
The only positive note for a disjointed home team was that they remained on level terms approaching the end of an unspectacular opening quarter.
Wales appeared gripped by nerves and hesitancy ahead of Gatland's squad announcement, with mistakes riddling their performance. It was a fact underlined when Byrne kicked into touch on the full under no pressure from outside his 22.
Contepomi broke the deadlock 10 minutes before half-time, although he needed a slice of fortune when his angled penalty went over via an upright.
It was a deserved lead for the Pumas, who continued to enjoy territorial supremacy, but Wales hit back on the stroke of half-time with a stylish response.
Their forwards initially made the hard yards, with lock Jones delivering a scoring pass to Powell, who galloped over from 20 metres out.
And before Argentina could recover, Jones found himself on the end of North's pass as Wales posted a second try in 90 seconds, both converted by Hook.
Argentina made two half-time substitutions, which included a chance for their former Northampton forward Scelzo, but Wales continued to build, with a 47th-minute Hook penalty making it 17-3.
The Pumas, having conceded 17 points so quickly, began to lose their shape, and Wales could sense more scoring opportunities as they grew increasingly confident with ball in hand.
Hook sacrificed a kickable penalty by opting for touch deep inside Argentina's 22 instead, yet even though Wales lost the ensuing lineout, they were soon back on the front foot.
Another successful Hook penalty took Wales into a 20-3 lead, and there appeared no way back for the Pumas, whose early promise had evaporated.
Things went from bad to worse for the visitors when their experienced number eight Juan Martin Fernandez Lobbe was sin-binned by referee Romain Poite after taking out Jones in mid-air.
It was the cue for a double Welsh substitution as an out-of-sorts Byrne made way for Aled Brew - Leigh Halfpenny went to full-back - and Jonathan Thomas replaced flanker Dan Lydiate.
Further Welsh changes ensued, including Test debuts for scrum-half Lloyd Williams and flanker Justin Tipuric, and Wales quickly added a third try through the impressive North.
Argentina, by now well beaten, then produced a close-range consolation try for Scelzo that Contepomi converted, before Hook ended the scoring by completing his penalty hat-trick.
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