Thiam posted a time of 13.54 seconds in the hurdles, her second best career time, 0.20 seconds above her personal best set in Götzis this year (13.34). This put her in eleventh place, but next came Thiam's specialty: the high jump.
Thiam cleared 1.95 metres to win it, failing three times on 1.98. Rodriguez improved her personal best with 8 centimetres to come second, also clearing 1.95.
Thiam has 2.215 points now, holding a small margin over Rodriguez (2.207). Germany's Caroline Schäfer is third with 2.165 points.
One of the contenders for the Gold, Laura Ikauniece-Admidina, was forced to pull out after injury. Katarina Johnson-Thompson of Britain had to be content with just 1.80 metres in the high jump.
The heptathlon will continue tonight, with the shot put and the 200 metres.
In the men's 400 metres, both Jonathan and Kevon Borlée qualified for tomorrow's semi-finals.