Tymoshenko also sought to spring a trap for former Prime Minister Viktor Yanukovich by inviting him to take part in a live television debate ahead of Sunday's poll.
But the Yanukovich camp, mindful of his often stumbling public performance, declined.
Tymoshenko, who led tens of thousands in mass protests in 2004 against electoral fraud, focused her attack on Yanukovich and his wealthy backers whom she described as an "oligarchic plague of locusts".
Yanukovich, who will likely face Tymoshenko in a run-off second round poll on 7 February, was the main loser in the 2004 'Orange Revolution' that brought President Viktor Yushchenko to power. After weeks of protests, a court ruled that a second round of voting had been rigged and ordered an unprecedented third round.
"If fraudulence is revealed, if we are unable to defend an honest result and prove that there was falsification, then we will resort to the courts," Tymoshenko told 5th TV channel on Sunday night.
"We will protect the country from a second coming of this oligarchic plague of locusts because they can eat up everything, but we must defend the country," she said.
Yanukovich, who represents the business interests of several big industrialists in the east of the country, has the backing of metals-to-banking billionaire Rinat Akhmetov and others in his second bid for the post of president.
Yanukovich had Moscow's backing for his bid for the presidency in 2004 and was tagged a pro-Moscow stooge after the Kremlin rushed to congratulate him prematurely on his election victory.
This time around, Moscow has gone out of its way to say it is not getting involved in Ukraine's election. The signs are that Moscow would prefer to do business with Tymoshenko, though Russian Prime Minister Vladimir Putin has denied Moscow is taking sides.
Issuing the challenge for an "open and honest debate" on television before the poll, Tymoshenko, herself a slick public performer, said: "Since he says he would be a strong president, I want him to show that at least he is not a coward and agree to a debate."
But Yanukovich, who often stumbles in his delivery and is prone to glaring errors of fact, side-stepped the trap.
Yanukovich was ready to compete with Tymoshenko "by good deeds and not beautiful words," Anna Herman, his close ally in the Party of the Regions, told Interfax-Ukraine news agency.
"If there was a world championship for beautiful unfulfilled promises then Yulia Tymoshenko would be without a challenger," Herman said.
(EurActiv with Reuters.)
