UPDATE 1-Sao Tome's Pinto da Costa wins presidential runoff
* Former post-independence communist leader wins vote
* Pinto da Costa pledges to fight corruption, poverty
* Concerns over slide back to authoritarian rule -analyst (Adds details, analyst comment)
By Ricardo Neto
Sao Tome, Aug 8 (Reuters) - Manuel Pinto da Costa has won a presidential election runoff in Sao Tome and Principe, the election commission confirmed on Monday, returning to power again in the tiny Gulf of Guinea island state after two decades.
Pinto da Costa, a 74-year-old economist by training, ruled the former Portuguese colony as a single-party state from independence in 1975 until 1991.
Sao Tome's national elections commission said Pinto da Costa won Sunday's second round vote with 52.88 percent against his opponent, parliament speaker Evaristo Carvalho.
IHS Africa analyst Sebastian Boe said Pinto da Costa's victory signalled the frustrations of the country's voters with the graft and mismanagement plaguing the country.
He said the election also raised concerns that the country might slide back to the authoritarian rule seen during Pinto da Costa's previous period in power. Continued...