Khama, the son of founding president Seretse Khama, quarrelled with Masisi over cabinet posts and the new president's controversial scrapping of an elephant hunting ban in May, which Khama had enforced four years earlier. Elephants, however, have not been an issue during the campaign.
The main concerns for the Batswana are unemployment hovering at around 20% and stark inequalities despite equitable state spending on health and education. To tackle either, the winner will need to do more to diversify the economy.
Mbakisi Gopolang, 25, waiting in line to cast his vote at a primary school in the capital Gaborone, said he was disappointed by the last decade under the governing BDP.
"The last ten years have been regressive, so I don't want continuation of that. I am voting for a party that will drive economic growth, empower citizens and get rid of corruption and bring about transparency."
Diamond mining has fallen to a fifth of GDP in 2018, compared with half in the 1990s, but it still makes up three quarters of foreign exchange earnings, even as banking and tourism grab a greater share of output.