BEIJING — Second-ranked Argentina was held to a 2-2 draw by the United States on Sunday and three-time Olympic champion Australia needed four unanswered goals in the second half to clinch a 5-4 win over South Korea on the opening day of the women's Olympic field hockey tournament.

Angie Loy leveled in the 64th minute for the Americans in a surprising result in the rain.

Argentina's Carla Rebecchi scored two goals in the first 12 minutes, and her team threatened to score several more times before the U.S. replied. Keli Smith scored after a penalty corner in the 18th minute.

Casey Eastham scored the winner in the 65th for Australia, which rallied from a 4-1 halftime deficit.

Shelley Liddelow, who scored once in each half, said it was a "good game to get out of your system."

Australia captain Nicole Hudson said the comeback win showed the character of the team.

"That felt like a final," she said. "This will be a very positive influence on our team.

"We said at half time 'if they can score four goals in the first half, we can do the same in the second' — and we played so well."

In other matches, Japan held on in a scoreless second half to beat New Zealand 2-1 and China beat Spain 3-0.