Germany is the reigning men's Olympic champion, but since its win in Beijing has looked increasingly unsteady compared to an improving Australia side. The Aussies beat Germany in the 2010 World Cup in New Delhi to underscore their gold medal potential in London.
"We've won everything in the last three years under Ric (Charlesworth, the Australian coach). We don't expect it to be easy, but we're going to concentrate on what we can do," Australia midfielder Jamie Dwyer said.
Australia has won the Champions Trophy every year since 2008. Germany could manage only fifth place in the 2011 competition.
But German captain Maximilian Mueller does not seem worried about his team's prospects, saying: "We are at our experienced peak and it is time to win something."
Second at the 2011 Champions Trophy was a Spain team that has looked dangerous since its 1-0 loss in the 2008 Olympic final.
"Our aims are to finish in the top two of the group so we can reach the semifinals," Spain coach Dani Martin said.
The Netherlands will also be disappointed to leave London without a medal, having been one of hockey's dominant teams for over two decades. But the Dutch men's team has not won gold since Sydney, where it successfully defended the Olympic title it won four years earlier.
In the women's tournament, Argentina and the Netherlands look to be closely matched. The Dutch are the reigning Olympic champion, but Argentina has looked impressive since its bronze in Beijing, winning the 2010 World Cup and the Champions Trophy earlier this year. Coach Carlos Retegui said the mood in the Argentina camp is "calm and content."
The Netherlands team will be helped in London by short corner specialist Maartje Paumen, the current world player of the year.
Paumen, the Dutch captain, broke the Olympic scoring record in Beijing with 11 in seven matches, including a hattrick in the Netherlands' 5-2 victory over Argentina in the semifinal.
Paumen needs three more goals to overtake Australia's Alyson Annan as the top Olympic scorer of all time.
Great Britain and New Zealand are the clearest challengers to the two-team dominance of the women's tournament. New Zealand is expected to significantly improve on its last place in the 2008 Olympics. The team won bronze medal in the 2011 Champions Trophy.
Host nation Great Britain has not won an Olympic women's hockey medal since its bronze in 1992, but will hope to reach the podium after a promising display in this year's Champions Trophy, in which it lost 1-0 to Argentina in the final.
"I think we're in that nice position where we're still an underdog, but we've had some good results and we feel confident," Great Britain captain Kate Walsh said.
The London Games mark the Olympic debut for the Belgium women's hockey team, which despite being ranked 16th is still "very ready" to face the Netherlands in its first game, according to coach Pascal Kina.
It is also the first time Olympic hockey will be played on a pitch that is not green — London's Riverbank Arena pitch is bright blue surrounded by pink. The new colour scheme is intended to make the game easier to follow for television viewers and spectators.
South Korean men's head coach Seokkyo Shin described the water-based artificial turf pitch as "very good — the blue and pink is very beautiful."
Women's hockey starts Sunday and the men's tournament begins Monday.