Mr Mwanawasa, in power since 2001, faces a strong challenge from the Patriotic Front leader who says the president's control of inflation means little when two-thirds of the population survive on less than a dollar a day.
"We need to bring hope to Zambia. Zambia has lagged behind in the region," Mr Sata told reporters as he voted in Lusaka. "Can people eat inflation?"
Polling booths closed at 6:00 pm on Wednesday after 12 hours of voting, with the 3.9 million-strong electorate voting not only for a president but also for members of parliament and local councils.
"Generally the voting went off smoothly. Although we did have some hiccups here and there, they were not major," said Electoral Commission of Zambia spokesman Chris Akafuna.
Although there were no turnout figures, observers said it appeared to be high.
"The level of participation is very high but I cannot give you a percentage," said Annemie Neyts, head of the European Union's mission.
"As far as we know there have been no serious incidents," she added.
With no consensus in the polls about a winner in the presidential race, counting began immediately after the close of voting. Full results are not expected until later on Friday at the earliest.
Mr Mwanawasa is banking on his image as a safe pair of hands and can point to a 4.9-percent rise in gross domestic product in 2005. He has also managed to keep inflation in single digits, in contrast to neighbouring Zimbabwe, where it recently hit a world record 1,200 percent.
Throughout the campaign, he has been urging voters to give him and his Movement for Multi-Party Democracy (MMD) more time to make further inroads against poverty, acknowledging he has only just "scratched the surface".
Mwanawasa refused to talk to reporters as he voted, citing regulations barring discussion of voting within 200 metres of polling booths.
Kenneth Kaunda, the former Northern Rhodesia's president from independence in 1964 until being ousted by the MMD in 1991, also refrained from declaring how he voted despite earlier endorsing long-shot candidate Hakainde Hichilema.
Mr Sata, who served under Mr Kaunda, has provided the campaign fireworks with assaults on foreign firms who run the country's copper mines as well as accusing Mr Mwanawasa of turning Zambia into the poor relation of southern Africa.
Nicknamed King Cobra, Mr Sata has combined attacks on Mr Mwanawasa's policies with less than subtle references to his health after the 59-year-old president suffered a stroke in April.
While Mr Mwanawasa and Mr Sata are seen as the main contenders, Mr Hichilema, a political novice with a background in accountancy, has built up support by portraying himself as a sound economic manager.
Two other candidates, Ken Ngondo of the Old People's Congress and Godfrey Miyanda of the Heritage party, are deemed to be rank outsiders.