The 18-year-old Das clocked 52.10 seconds to win the semifinals heat number one and led the overall time charts. She had also led the time charts in the first round heats yesterday with a timing of 52.25.
Another Indian in the fray, Jisna Mathew, however, failed to make the finals after finishing fifth in semifinals heat number 2 with a time of 53.86 and 13th overall.
The first two finishers in each of the four heats and the next two fastest qualify for the final which will be run tomorrow.
Das is a favourite to win gold as she is the U-20 season leader in this quartermile event. If the Assam girl happens to win gold, she will become the first Indian athlete to do so in a track event in an U-20 World Championships.
Das clocked an Indian U-20 record of 51.32 seconds to finish sixth in the Commonwealth Games 400m final in Gold Coast in April. Since then, she has gone onto improving her timings. She lowered the Indian U-20 record in 400m to 51.13 seconds while winning gold in the recent National Inter State Championships in Guwahati.
In men's 400m, Gaurav failed to progress further as he finished fifth in his heat and 42nd overall with a time of 48.61.
Shot putter Ashish Jakhar also made it to the final round after finishing eighth overall in the qualification round with a throw of 70.52m while compatriot Damneet Singh (67.48) crashed out after finishing 15th.
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