Winger Sebastian Cancelliere, centre Matias Orlando and hooker Agustin Creevy scored first half tries for the home side at Velez Sarsfield in Buenos Aires, with Miotti adding five points with the boot, which included the only points in the second half with a penalty.
Hooker Folau Fainga'a and fullback Tom Banks scored for the Australians, while first-five Christian Lealiifano added a conversion and penalty for the visitors, who wasted several opportunities to add to their halftime score.
The second half developed into a battle of attrition and involved some bad tempered scuffles, with Miotti's penalty giving his side their five-point advantage heading into the final quarter.
STORMERS 24 BULLS 23
Dillyn Leyds put in a man of the match performance as the Stormers breathed new life into their ailing Super Rugby campaign with a narrow victory over the Bulls in a fierce South African derby at Newlands on Saturday.
The Cape Town-based side have failed to live up to their promise this season and were on a run of four defeats in five games, but showed the greater physicality and execution to claim what could turn out to be a precious win.
Leyds proved the playmaker in the back line, but their tries were scored by wings Sergeal Petersen and Seabelo Senatla, while scrumhalf Hershel Jantjies did his Springbok chances no harm with a lively performance that was capped with a third try.
The Bulls overcame a poor start to stay in the contest, and grabbed a losing bonus-point when replacement Manie Libbok crossed for a converted try in the final play of the game.
WARATAHS 15 SHARKS 23
Flyhalf Curwin Bosch kicked two late penalties that helped the Sharks to victory over an ill-disciplined Waratahs, who were at one stage reduced to 13 men, in their clash in Sydney on Saturday. The Waratahs lost Jed Holloway when he was sent off by referee Nic Berry for striking Sharks prop Thomas du Toit with his elbow in the 46th minute.
Berry gave Waratahs flanker Jack Dempsey a yellow card five minutes later for a dangerous tackle on Sharks winger Sibusiso Nkosi.
Centre Andre Esterhuizen scored a try when the Sharks held a two-man advantage, while Bosch added the two late penalties to hold on for victory after the game had been locked at 10-10 at halftime.
HURRICANES 47 CHIEFS 19
Jordie Barrett reminded All Blacks coach Steve Hansen of his World Cup aspirations as he scored two early tries to help the Hurricanes beat the Chiefs on Saturday.
Barrett, who has played fullback and on the wing for the All Blacks, reminded Hansen of his own credentials in the number 15 jersey in his first appearance there for the Hurricanes since week two. He finished the game in the midfield, where he has played two games this season.
Kane Leaupepe, TJ Perenara, Wes Goosen, Ardie Savea and debutant Salesi Rayasi also crossed for the home side, who moved to 32 points and consolidated their hold on second place in the New Zealand conference behind the Canterbury Crusaders (39).
Luke Jacobson, Ataata Moeakiola and Lachlan Boshier all scored tries for the Chiefs, who had given the Hurricanes a 21-0 lead after 17 minutes before they managed to fight back and keep it tight until early in the second half.
SUNWOLVES 0 HIGHLANDERS 52
Tevita Li scored two tries as he capitalised on the dominance of a Highlanders pack led by a rampaging Jackson Hemopo to help the visitors to a commanding victory over the Sunwolves in Tokyo on Friday.
The visiting team's forwards obliterated the Sunwolves scrum at will, even after they had replaced their entire front row, and dominated the contact area to force errors, moving back into playoffs contention in fifth place overall on 23 points.
The Highlanders scored five tries in the first half from Tom Franklin, Tyrel Lomax, Li, Josh Ioane and Liam Coltman to give them a 33-0 lead at the break.
Li grabbed his second try about 10 minutes into the second half before Rob Thompson and Sio Tomkinson also crossed, while the home side were unlucky to have a Semisi Masirewa try ruled out for a forward pass.
CRUSADERS 36 LIONS 10
Sevu Reece crossed for two tries and set up another for Braydon Ennor as the Crusaders sent a chilling message to the rest of the Super Rugby teams with a convincing victory over South Africa's Lions in Christchurch on Friday.
Reece was a late call-up by the Crusaders this season after he had a contract in Ireland cancelled due to a court appearance for assaulting his girlfriend. He has taken his second chance at a professional career with both hands.
George Bridge also scored two tries within the space of two second-half minutes while Richie Mo'unga celebrated his 50th appearance and a new three-year contract with 11 points for the nine-times champions.
Ruan Combrinck scored an intercept try for the visitors, who had lost to the Crusaders in both of the last two finals and while they caused some issues at the scrum, they were rarely able to put sustained pressure on the home side.