She followed closely by a pack of nearly 15 athletes spread over 17 seconds .
In the first semifinal , Hungary 's own Margit Vanek led out of the three - lap 750m swim .
Margit Vanek followed closely by a pack of nearly 15 athletes spread over 17 seconds .
In the first semifinal , Hungary 's own Margit Vanek led out of the three - lap 750m swim .