The September 30 elections were called by President Viktor Yushchenko in the hope that they would end a standoff with his arch-rival, Prime Minister Viktor Yanukovych.
Now Yushchenko finds himself sidelined as Yanukovych and his former ally, Yulia Tymoshenko, claim victory.
Preliminary results initially gave the Yulia Tymoshenko Bloc a slight lead. But as vote counting moved from the country's Europe-leaning west to its Russian-speaking east, the balance tipped back in favor of Yanukovych's Party of Regions.
With 87 percent of ballots counted, the prime minister's pro-Russia party leads with 33.2 percent.
Tymoshenko's pro-Western bloc is close behind with 31.5 percent of the votes.
Yushchenko's pro-presidential bloc, Our Ukraine-People's Self-Defense, is a distant third at 14.7 percent.
A beaming Tymoshenko had declared victory overnight after exit polls gave her opposition bloc and the pro-presidential bloc just enough seats combined to form a governing majority.
"In these parliamentary elections, Ukraine's democratic forces won again, and together we, as usual, gained more votes than our opponents," she said. "This is very pleasant, and I would like to greet the president and all our democratic team with the obvious victory."
Her strong showing marks a striking comeback for Tymoshenko, who announced that she intended today to offer Yushchenko to form a coalition government.
A new coalition would reunite the team that swept to power during the 2004 Orange Revolution, when demonstrators took to the streets in Kyiv to contest a rigged presidential election won by Yanukovych.
A court-ordered rerun gave the victory to Yushchenko, who named Tymoshenko prime minister. The duo soon had a falling out, with the president dismissing Tymoshenko after just nine months in office in a dispute over economic policies.
But Tymoshenko's prediction that the new coalition would hold its first government news conference "in a matter of weeks" may have proven hasty.
Yanukovych's party is a force to be reckoned with, particularly in combination with other, smaller parties.
One of them is the centrist bloc of former parliament speaker Volodymyr Lytvyn, which has an unexpected 4 percent in preliminary vote counts and has said it might join either camp.
Another is the Communist Party, which looks like it will easily clear the 3 percent hurdle for parliamentary representation with 5.2 percent of the vote.
Speaking today in a televised statement, Yanukovych criticized Orange forces for rejoicing too soon:
Tymoshenko declared victory overnight (AFP)
"The Orange made premature conclusions and sought to further split Ukraine and its people by their hasty statements," he said.
Tough Talks Ahead
A top Tymoshenko ally, Oleksandr Turchinov, said her bloc may challenge the prime minister's showings in eastern Ukraine due to what he said were attempts to rig the vote. Yushchenko, meanwhile, ordered Ukraine's security forces to immediately investigate delays in the vote count in eastern and southern Ukraine.
But with the Organization for Security and Cooperation in Europe endorsing the vote as overall free and fair, even a partial repeat of the elections is unlikely.
Some political analysts have even suggested that Tymoshenko could eventually walk out on Yushchenko and opt for the more popular Yanukovych as a coalition partner.
Should Tymoshenko and Yushchenko chose to revive the spirit of the Orange Revolution, will the former allies be able to put aside old grievances?
RFE/RL analyst Jan Maksymiuk says coalition talks between the Yulia Tymoshenko Bloc and Our Ukraine would certainly be thorny:
"Both parties have a coalition agreement signed earlier this year which says that they may form a government on a 50-50 basis," he says. "But at that time, I think Yulia Tymoshenko did not foresee that she will actually be the election's only winner. Now that her performance is so strong, I think she may correct her coalition agreement with Our Ukraine. So it won't be easy for them to strike a coalition."