Isinbayeva, who holds the outdoor world record of 5.06 metres and was virtually unbeatable in the discipline between 2003 and 2008, has not won a global title since Olympic gold five years ago in Beijing.
The 31-year-old had said she will end her illustrious career after the competition at the Luzhniki stadium, although she rowed back from that after qualifying by saying her mind was not yet made up.
While Isinbayeva contemplates retirement, the precocious Kirani James, 20, is set to continue his global domination of the men's 400 metres by adding a second world gold.
The Olympic champion has American LaShawn Merritt - the only man to beat the Grenadian this season - to contend with.
In the absence of injured Olympic champion and world record holder David Rudisha, the men's 800m title is wide open, although Ethiopia's 19-year-old 2012 world indoor winner Mohammed Aman has enjoyed an impressive season.
Americans Duane Solomon and Nick Symmonds, along with Saudi Arabia's Abdulaziz Ladan Mohammed should provide the main threat to the African.
The women's 3000m steeplechase final has also been robbed of a marquee name after Russia's Olympic and world champion Yuliya Zaripova of Russia had to withdraw after suffering a season-ending leg injury in training.
Ethiopian duo Sofia Assefa and Hiwot Ayalew, Kenya's African record-holder Milcah Chemos Cheywa - the last woman to beat Zaripova - and compatriot Lydia Chepkurui should fight it out for the medals.
Briton Mo Farah, having secured 10,000 metres gold on Saturday, starts his bid to repeat his Olympic distance double when he lines up in the morning's 5,000m heats.
In the men's discus final, Germany's Robert Harting starts as hot favourite to secure a third successive world title, although the Olympic and European champion could be tested by Pole Piotr Malachowski.
Golds in the heptathlon and women's 20-km walk will also to be decided today.
