Germany’s Carolin Schaefer, the leader from day one, dropped into the silver medal position after the first event of the day and only just managed to stay ahead of Vetter after a brilliant performance by the Dutch athlete in the javelin.
The 24-year-old was already leading the round but then managed a colossal throw of 58.41 metres on her final attempt, a championship record, to climb up to third place on 5805 points with just the 800 metres race remaining.
Thiam, Olympic champion in Rio last year, built on her lead at the top with a throw of 53.93 to finish the session on 5980 points.
Schafer is just three points ahead of Vetter, but will be hopeful of securing silver in the 800m, having a better record than her rival in the event.
Despite Vetter's javelin heroics, the bronze medal is still up for grabs. Cuba’s Yorgelis Rodriguez sits fourth on 5636 and home favourite Johnson-Thompson is on 5565. Both women are strong competitors in the final event which takes place at 1940 GMT.
The heptathlon climax will come after the reallocated medal ceremony for the Daegu 2011 competition.
Britain’s Jessica Ennis-Hill will be upgraded from silver to gold and Jennifer Oeser of Germany from bronze to silver following former champion Tatyana Chernova of Russia’s positive test for a banned anabolic steroid in January 2015.
(Reporting by Christian Radnedge; Editing by Toby Davis)
