Hosts Argentina, who beat China 2-0, have a maximum 12 points with England, 2-1 winners against South Africa, on 10.
South Korea are third with five points after being held 2-2 by bottom team Spain. China and South Africa have three points each.
Argentina finally broke down a stern Chinese defence in the 51st minute with a penalty corner goal by their specialist Noel Barrionuevo, whose tally is now four.
They went further ahead when captain Luciana Aymar, six times world player of the year, scored a brilliant second goal after dribbling her way through the Chinese defence to also take her tournament tally to four.
"I was marked all match and then I saw the gaps and said to myself 'why don't you score too'," said Aymar on Argentine television of her run before steering the ball past goalkeeper Li Dongxiao from a narrow angle.
England beat South Africa 2-1 with Helen Richardson scoring a first-half field goal and converting from a second-half penalty corner to take her tournament tally to three.
Pietie Coetzee replied late for South Africa deflecting the ball in from a penalty corner for her third goal.
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