Vietnamese defending champion Nguyen Thi Thanh Phuc lost her 20km walk title at the SEA Games in Myanmar Sunday under controversial circumstances.
After the race she said the winner, the host country's Saw Mar Lar Nwe, "walked and ran, walked and ran, but the judges gave her only two [red] cards."
A third violation would have seen her disqualified.
Thanh Phuc could only finish second and burst out in tears at the finish.
Vietnamese coach Tran Anh Hiep said: "In the track and field event, Myanmar could only expect to win the gold medal in the walk, so they did everything possible to win. We had expected some difficulty competing against the hosts in this event."
Phuc had been training hard for two years to defend the title, he added.
Contestants must have one foot on the ground at all times and straighten the front leg.
In other action, 16-year-old Lam Quang Nhat upset stronger swimmers to grab the 1500m men's freestyle gold.
Nhat, who had finished fourth in the heats, swam the distance in 15 minutes 39.44 seconds while Malaysia's Kevin Yeap came second.
Vietnam won seven golds on Sunday to take their tally to 36. They are in third place behind Thailand with 45 and host Myanmar with 38.