Yuri Sukhanov, who was installed as head of the state-owned firm on May 13 but was locked out of Slavneft's office building in Moscow since last week by his predecessor, re-entered the premises, a company spokeswoman told AFP.
His rival, Mikhail Gutseriyev, who was ousted from the helm of the company in favor of Sukhanov, found the tables turned after having seized control of Slavneft last week with the help of armed police.
Despite reportedly enjoying the backing of a powerful clique from President Vladimir Putin's hometown of St. Petersburg, Gutseriyev no longer had access to the firm's office on July 2 and was losing the legal initiative.
Sukhanov took over control of the building in the morning accompanied by high-ranking police officials.
Russia's Justice Ministry meanwhile announced that it had asked the Supreme Court to intervene to stop rival managements misusing court judgements to challenge the outcome of shareholder meetings, in particular in relation to Slavneft.
The conflict is bound to put off foreign investors in Russia and has thrown into doubt the government's plans to sell off a 20 percent stake in Slavneft later this year, say analysts.