The Services managed only two penalties, but for a side containing only two players from clubs higher than Courage League Three, did well to hold a team virtually full of Test players to 14-6 until the half-hour mark.
After that the Pumas really opened it up, running their penalties and spreading the ball wide at speed. Their first try came in the 10th minute. A typical running move ended with a long pass to wing Facundo Soler who crossed. Four minutes later the lock Jose Simes rounded off a series of drives and a break by the No 8 Pablo Bouza to score.
Despite being opposed by a brave, tireless pack, the Pumas made use of the plentiful loose ball they got to run in two more first-half tries from Bouza and the centre Francisco Garcia.
After the break, the wing Diego Albanesi touched down and the captain, Lisandro Arbizu, crossed after Knowles had been clattered on his own line, before the flanker Martin and the hooker Carlos Promanzio brought up the half-century of points.
Western Samoa gained their seventh win in 10 tour games, beating a Leicester/Northampton Select XV 33-20 at Leicester last night. The Sam-oans scored five tries to two and though the home side came back from 20-6 down at half-time to be within three points at 20-23, the tourists deserved to win.
Queensland made it six victories in a row on their British tour as they came from behind in the second half to win 28-19 at Pontypridd, who chose to risk only two first-team regulars before Saturday's key First Division game with Bridgend.
n Jonah Lomu played for Ebbw Vale last night in their 65-59 defeat by a Welsh Invitation XV.