Both Yushchenko and Yulia Tymoshenko, the premier he sacked in September, told supporters in Kiev's Independence Square that only a united team of reformers could win the March 2006 election to a parliament led by a prime minister with expanded powers.
But Tymoshenko's impassioned 20-minute address, delivered without notes, clearly won over a crowd of well more than 100,000 marking last year's mass protests which helped propel the president to victory in the re-run of a rigged poll.
"I am certain that just as we supported Viktor Yushchenko in the presidential election, we must now unite to elect a prime minister who will embody everything we fought for," Tymoshenko, tears welling in her eyes, told the crowd.
"I want to dismiss all the rumours that it is Tymoshenko versus Yushchenko. This cannot be so, because this is the president that you and I helped bring to power. We did it together."
Tymoshenko's speech on what the liberal administration has proclaimed "Freedom Day" was clearly aimed at the March election campaign.
It also sought to justify her eight months in charge of a government that blew apart after splitting into rival camps, each accusing the other of corruption.
As snow fell on the square, she told supporters: "My heart is with you. If it didn't work the first time, it will next time round. We cannot stop with things half finished."
PUBLIC CONFIDENCE SAPPED
Tymoshenko's dismissal dented the ratings of both leaders. It also sapped public confidence among Ukrainians who had backed the ideals of mass protests against election fraud and Yushchenko's calls to move Ukraine into the European mainstream.
The Regions Party of Viktor Yanukovich, the rival Yushchenko defeated in last year's lengthy election campaign, leads polls for the March contest with more than 20 percent support.
Tymoshenko's Fatherland Party lies second with 17 percent and the pro-presidential Our Ukraine commands about 12 percent.
Yushchenko looked distinctly uncomfortable, issuing a similar call for unity at the end of an hour-long speech interrupted periodically by hecklers shouting "Yulia, Yulia!"
"Do we want to win the 2006 parliamentary election? Yes, we do!" the president, accompanied on stage by his wife and children, said to modest applause from the crowd.
"This team standing behind me must be united, must work together and extend a hand to one another."
Tymoshenko, widely popular among rank-and-file voters for her rousing speeches during last year's protests, was appointed prime minister last February under an electoral pact.
During her tenure, Western investors took fright at calls for a sweeping review of privatisations conducted under the previous administration. She also clashed with Yushchenko over attempts to control fuel prices.
Her replacement, technocrat Yuri Yekhanurov, is seen as a transition figure before the March election brings in new arrangements handing many presidential powers to the prime minister and parliament.