By Tsvetelia Tsolova and Angel Krasimirov
SOFIA (Reuters) - Bulgarian Socialist ally Rumen Radev, a Russia-friendly newcomer to politics, won Sunday's presidential election by a wide margin, exit polls showed, prompting centre-right Prime Minister Boiko Borisov to pledge to resign.
Radev, 53, entered Bulgarian politics on a wave of discontent with the ruling centre-right's progress in combating corruption, disappointment with the European Union and concerns among voters over alienating an increasingly assertive Russia.
A former air force commander, Radev has argued Bulgaria needs to be pragmatic in balancing the requirements of its European Union and NATO memberships while seeking ways to benefit from a relationship with Moscow.
Exit polls showed Radev, who is backed by the opposition Socialist party, winning 58.1-58.5 percent of the vote, compared with 35.3-35.7 percent for Tsetska Tsacheva, the 58-year-old candidate of the ruling GERB party.
Compounding GERB's problems, Tsacheva was seen as lacking Borisov's charisma.
"The loss of GERB is definite and clear," Borisov told reporters after exit polls were published.
"In this election, the people showed us that something is not as it should be. That our priorities may be good, but obviously there are better ones. So the most democratic thing, the right thing to do is to (resign)," he said.
Borisov's resignation would likely lead to an early election as soon as March and could be followed by months by difficult coalition talks among several political groupings.
"There isn't an alternative to take over government," said political analyst Ognian Minchev. "The Socialists and the ethnic Turkish MRF party have lost much of their public trust only two years ago...Early elections are inevitable," he said.
FINDING A BALANCE
Coupled with political instability, Bulgaria's tilt toward Russia is a blow to the country's western European allies and underscores Moscow's growing influence in southeastern Europe.
In Moldova, another ex-communist state near the Black Sea, voters were expected to install a pro-Russian candidate as president and slam the breaks on seven years of closer EU integration in an election also held on Sunday.
While most of the key decisions in Bulgaria are taken by the government, the president, who leads the armed forces, can sway public opinion and has the power to send legislation back to parliament.
Radev is not advocating NATO member Bulgaria abandon its Western alliances, mindful of the financial impact of EU aid and the country's long history of divided loyalties.
But he has called for an end to EU sanctions against Russia and said Sofia should be pragmatic in its approach to any international law violations by Moscow when it annexed Crimea.
"We listened (to the voters') concerns. We said that we will work for Bulgarian national interests, that's what gave us broad support," a jubilant Radev told reporters.
Many in the Balkan country are keen to see restored trade with their former Soviet overlord, hurt by economic problems and sanctions, and to protect vital tourism revenues.
Speaking on Sunday evening, Radev said he hoped for good dialogue both with the United States and Russia and expressed hopes that with a new president in Washington, there will be a drop in confrontation between the West and Moscow.
"In his election campaign (Donald Trump), already elected, said clearly that he will work for a better dialogue with Russia. That gives us hope, a big hope, for a peaceful solution to the conflicts both in Syria and in Ukraine and for a decrease of the confrontation," Radev said.
Although Bulgaria's economy is expected to grow at a relatively healthy rate of about 3.1-3.3 percent this year, having shaken off recession, it remains the EU's poorest member, with average wages about 470 euros per month.
Rampant graft in public administration is seen as a key factor slowing the small Black Sea state's progress in catching up with its wealthier EU peers.
(Additional reporting by Radu Marinas; Editing by Dale Hudson, Justyna Pawlak and Alexandra Hudson)