Luka clocked 2:02.71 secs behind Cuban Yuneisy Santiusty (2:00.93 secs) and Marta Milani (2:02.65 secs) of Italy.
Luka has already crossed the London Olympics 'B' mark of 2:01.30 secs though she is yet to touch the 'A' standard of 1:59.90 secs.
She had clocked 2:01.09 secs in the first leg of the Samsung Diamond League series last month.
Luka holds the national record of 1:59.17 secs but is yet to run sub two seconds this season, with London Olympics just a month away.