The tiny margin in favour came as a surprise, although Maia Sandu said there was clear evidence of attempts to buy 300,000 votes.
The BBC spoke to one voter who said she and others had sold their votes for up to 1,000 roubles (£8).
Whatever Russia’s role behind the scenes, police said fugitive oligarch Ilan Shor had moved $39m (£30m) over two months from Moscow into Moldovan bank accounts in September and October, benefiting at least 138,000 voters.
Shor denies wrongdoing but did promise cash handouts to people prepared to back his call for a “firm No” to the EU. He faces a lengthy jail sentence in Moldova for money laundering and embezzlement.
Stoianoglo denies links to Ilan Shor but he does have the backing of the opposition pro-Russian Party of Socialists, led by ex-president Igor Dodon.
A populist ex-mayor who came third has refused to back either him or Maia Sandu, criticising both in equal measure.
“Do what you see fit. You must decide on your own,” Renato Usatii told his supporters, blowing the race wide open.
