With more than 90 percent of ballots counted, Central Election Commission data showed Dodon winning 36 percent against Sandu’s 32 percent.
A candidate needs more than 50 percent of the vote to avoid the November 15 runoff.
In 2016, Dodon defeated Sandu in a second-round runoff by less than 5 percent in an election that was marred by allegations of fraud.
Political analyst Valentin Naumescu told RFE/RL’s Moldovan Service that the outcome of the first round was “predictable.”
He suggested Dodon is likely to strengthen his position and win the runoff.
With a population of about 3.5 million, Moldova is Europe’s poorest country and is sharply divided between those who support closer ties with Russia and those who advocate links with the European Union and, especially, neighboring Romania.
The country’s Moscow-backed breakaway Transdniester region has been de facto independent since a separatist war in the 1990s.
A former World Bank economist and prime minister, Sandu has campaigned against corruption and called for closer ties with the European Union.
If elected, she has promised to secure more financial support from Brussels.
Dodon says he wants to reach a settlement next year for the Transdniester region
Dodon has run largely on a platform calling for “stability” and has promoted his record of securing loans and other economic favors from Moscow.
He has been criticized for his handling of the coronavirus pandemic, during which more than 55,000 Moldovans have been infected and more than 1,300 have died.
With reporting by RFE/RL’s Moldovan Service.