Alexander Korzhakov, a former close friend who is now one of Mr Yeltsin's fiercest opponents, won 26 per cent of Sunday's vote in the central Russian city of Tula, according to preliminary results.
The former KGB major took a leaf out of Mr Yeltsin's book for his aggressive campaign, bringing rock stars to the sleepy town and overwhelming the media with his advertising.
He emerged more than nine points clear of his nearest rival, local politician Eduard Pashchenko. Chess champion Anatoly Karpov was just behind in third place and Nikolai Novikov, a businessman who ran his campaign from a prison cell while awaiting trial for extortion, was fourth.
Some analysts predict that Mr Korzhakov will use the platform of the Duma and the immunity from prosecution enjoyed by deputies to step up his fight against Mr Yeltsin, who sacked him and other Kremlin hawks in June.
A close friend of Mr Yeltsin for 10 years, Mr Korzhakov has presented himself as a victim of a Kremlin plot and pledged to unveil "compromising material" against the establishment.
"I think he has enough material to make trouble for many Russian politicians," said Andrei Piontkovsky, of the Moscow Centre for Strategic Studies.
Last May Mr Korzhakov said he wanted the presidential election to be postponed, putting him on collision course with the liberal Anatoly Chubais, then effective head of Mr Yeltsin's campaign. Mr Chubais, now Kremlin chief of staff, has been called a regent by Mr Korzhakov, who says he has assumed huge powers since Mr Yeltsin fell ill in June.
Mr Yeltsin dismissed Mr Korzhakov before July's presidential runoff, which he won, and ordered an inquiry into the general's activities. Mr Korzhakov fought back by going to court and accusing Mr Yeltsin of defamation. There has been no decision yet.
Television channels, loyal to Mr Yeltsin, attacked Mr Korzhakov in a bid to put the voters off, but the residents of Tula showed the nationwide tendency to favour the candidate seen to carry political weight in the capital.
Mr Korzhakov promised to use his inside knowledge of the Kremlin to help Tula, a former defence industry centre suffering from the end of the Cold War. Voters turned out for his pre-election rallies eager to hear some Kremlin gossip, but Mr Korzhakov remained tight-lipped, saying he would only spill the beans once he was elected.