Great Britain's men matched the women by opening their Olympic campaign with a comprehensive victory, beating Argentina 4-1 at the Riverbank Arena.
Captain Barry Middleton scored either side of half-time before Dan Fox got his first international goal and Richard Smith made it four.
Pedro Ibarra's late penalty corner was only a consolation for Argentina.
Australia lead Pool A after hammering South Africa 6-0, while Spain and Pakistan drew 1-1.
Spain captain Santi Freixa was later ruled out of the rest of the Olympics after breaking his left arm in a collision with Muhammad Irfan.
Freixa played on in spells, at times one-handed, but was clearly in pain and team officials have confirmed he will be replaced by Andres Mir.
In the British men's first match of London 2012, Middleton made the breakthrough in the 23rd minute when he smashed home the rebound from a penalty corner, while his second came in the 41st minute after he was played in by Ashley Jackson.
In a feisty encounter, Matt Daly was sin-binned for a stick tackle before Agustin Mazzilli followed him for a sliding tackle on Iain McKay.
Fox then scored his first international goal after more excellent work from Jackson, who covered half the length of the pitch before setting up his team-mate, before Smith wrapped things up with a penalty corner.
Ibarra cut the deficit with 15 minutes left but soon found himself sin-binned on a miserable day for the Argentines.
Middleton denied that the match had been more physical because of bad feeling between the teams.
"This game for us was always about the sporting element," he said.
"We have never gone into any game against Argentina with anything other than hockey on our minds. There was some needle in the game but that is because this is an Olympic Games. If you didn't see that, I don't think we'd be putting in our all out there.
"We've put two years of our lives on hold to do this and I think that showed. The Argentinian guys are the same. It is a battle, it is hard, but no-one stepped over the line. There were some big tackles but everything was within the laws of the game."
Britain play South Africa in their next match at 16:00 BST on Wednesday.
In Pool B, South Korea beat New Zealand 2-0, the Netherlands edged out India 3-2 and Germany beat Belgium 2-1.