Three months after the biggest demonstrations in years prompted the former bodyguard to tender his government's resignation, Borisov's GERB party won between 30.3 and 33 per cent of the vote, the exit polls showed.
In second place was the socialist BSP party on between 25.3 and 27.1 per cent, followed by the Turkish minority party MRF on 6.5-11.5 per cent and the ultra-nationalist Ataka on 7.3-8.5 per cent.
As a result of the lack of a clear result, it remains unclear how these parties can form a government.
Analysts say that with no clear result, Bulgaria is likely to see a repeat of the protests that rocked the country over the winter and forced Borisov to throw in the towel.
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The protests saw seven people set themselves on fire, six of whom died.
Six years after joining the European Union, almost a quarter of Bulgarians live below the official poverty line, living standards are falling and poverty is on the rise.
The economy grew just 0.8 per cent in 2012 and foreign investment has slumped in recent years, sending unemployment up to almost 20 per cent, according to unofficial estimates.