irbsevens.com and James Mortimer 23.Mar.2013Getty Images
Paul Treu's side came into this tournament after an impressive victory against New Zealand in the Las Vegas final, but were unable to stop Los Pumas' captain Nicolas Bruzzone scoring two tries and now face matches with Australia and Wales on day two.
On an enthralling day of action which saw 28 teams competing, defending champions Fiji proved too strong for hosts Hong Kong.
Two tries each from Ilai Tinai, Benito Masilevu and Samisoni Viriviri assisted in the 36-0 victory for the islanders, who are currently fourth in the overall standings on the World Series.
Canada, who secured their place as a core team at last year's Hong Kong Sevens, impressively beat Spain 31-7 thanks to two tries from Taylor Paris.
Current Series leaders New Zealand, last year's runners-up, beat France 33-12 in Pool B, while Dennis Ombachi scored twice for Kenya to record a 17-14 victory against USA.
In one of the most entertaining matches of the day, Duarte Moreira scored four tries for Portugal as they dramatically beat Scotland 27-21 in Pool C.
With Scotland leading 21-20 thanks to two tries from Andrew Turnbull, Moreira dotted down in the corner to secure victory, before England were undone by an impressive Samoan performance in a 28-7 defeat.
In Pool A, Wales defeated Australia 19-14, despite two tries from Lewis Holland for Michael O'Connor's side.
In the 12-team pre-qualifier competition from which four will progress to the core team qualifier at the Marriott London Sevens, Rugby World Cup Sevens hosts Russia impressed in their 43-5 victory against the Cook Islands in Pool G.
Tafadzwa Chitokwindo scored the opening try of the tournament as Zimbabwe beat Mexico 27-0, also in Pool G, before next week's hosts Japan narrowly defeated the hosts of the 2016 Olympic Games, Brazil, 17-10, having come from 10-5 down at half time thanks to a hat-trick from Sione Faamao Teupa.
Irakli Machkaneli scored twice for Georgia as they beat Hong Kong debutants Jamaica 27-17 in Pool F, while Uruguay beat Chinese Taipei 24-12 and Tonga narrowly beat Tunisia 14-12 in Pool E.