Preliminary results after 87 per cent of votes counted put Stoianoglo, an ex-prosecutor-general, on 51.2 per cent, but the votes of Moldova's diaspora - who in the first round had favoured incumbent Maia Sandu - were yet to be counted.
Vlad Kulmninsky, a Chisinau-based political analyst, told Reuters he believed the early results indicated that Sandu had won Sunday's election. Neither Sandu nor Stoianoglo have commented.
Alexandr Stoianoglo has a slender lead as votes continue being counted. (AP PHOTO)
A former attorney general who is considered the pro-Russian candidate Stoianoglo, 57, stood for the Party of Socialists of the Moscow-friendly former president Igor Dodon.
The votes of hundreds of thousands of Moldovans abroad are likely to be decisive.
As election day progressed, Sandu warned against vote-buying and fraud.
Maia Sandu says Russia's interference in the election risks distorting the result. (AP PHOTO)
Her national security adviser, Stanislav Secrieru, accused Russia of massive interference in the ongoing runoff vote for the presidency.
Speaking on the X platform, Secrieru said that interference in the election posed a great risk of distorting the result.
with dpa