Results: Germany 0-0 Brazil, Japan 2-2 New Zealand, Argentina 1-2 Canada
China 2-1 Sweden, Norway 2-0 USA, North Korea 1-0 Nigeria
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Han's 101st international goal secured an opening win for China
Hosts China beat Sweden 2-1 as the women's football tournament brought the first action of the 2008 Olympic Games.
Han Duan's winner delighted a crowd of nearly 38,000 as the event kicked off two days before the opening ceremony.
Han's 72nd minute strike sparked boisterous scenes at the Tianjin Olympic Sports Center Stadium.
Meanwhile, Norway shocked defending champions the US with a 2-0 win, and Brazil held world champions Germany to a goalless draw.
The men's tournament begins on Thursday with eight matches across four venues, including favourites Netherlands taking on Nigeria and champions Argentina facing the Ivory Coast.
Argentina look set to be without Lionel Messi after his club Barcelona won an appeal to keep him out of the tournament.
China's women's team came into the event without Sun Wen, who shared the Fifa Woman's Player of the Century award.
However, they struck first in their opener against Sweden through a sixth-minute strike by Xu Yuan.
Lotta Schelin equalised in the 38th minute but China sealed victory when substitute Wang Dandan played the ball into the penalty area to Xu, who dropped it back for Han to strike her 101st international goal in 160 matches.
Victory over the 2004 semi-finalists gives China the upper hand in Group E. Canada beat Argentina 2-1 in the other game.
Group F remains wide open after Brazil exacted some revenge for last year's 2-0 World Cup final defeat by holding held world champions Germany to a goalless draw.
The match was played in front of a sparse crowd - including Brazilian star Ronaldinho - at the Shenyang Stadium.
North Korea beat Nigeria 1-0 in the second Group F game.
Wednesday's shock result came at the Qinhuangdao Olympic Sports Center Stadium where Norway stunned the reigning champions USA 2-0.
The Norwegians scored twice in the first four minutes through Laursen Kaurin's header and a solo effort from Melissa Wiik.