Isinbayeva, 31, lit up the Luzhniki stadium when she soared 4.89 metres on her first attempt and the American Olympic champion Jennifer Suhr and Cubas Yarisley Silva failed to follow.
Isinbayeva sprinted to her coach Yevgeny Trofimov even before Silva had landed after her final miss and hugged him - before missing three attempts at a world record 5.07m.
The Russian said after qualifying that she will not retire immediately but would like to have a family and a baby.
She said she aims to return for the Beijing 2015 Worlds and Rio 2016 Worlds, but only if all goes well.
The Volgograd resident is the face of athletics along with Jamaican sprinter Usain Bolt, and has ruled the pole vault with Olympic golds in 2004 and 2008 and world titles in 2005 and 2007, to go with a staggering 28 world records.
But she faded in recent years, taking 2010 off, returning to her long-time coach Trofimov, finishing only sixth at the 2011 Worlds and having to settle for bronze at the 2012 Olympics behind Suhr and Silva.