The former president warned that the Kenyan people "will be the losers if there is a descent into violence". The ethnic violence that followed killed 1,200 people and displaced 600,000.
However, some Kenyans are anxious by memories of the violent months that followed the 2007 vote and say there could be trouble ahead.
"We shall not accept to be rigged out.we will seek legal redress to see that justice is done".
A 102-year-old woman believed to be one of Kenya's oldest citizens said she voted for Mr Kenyatta.
This year, security chiefs say there will be 180,000 officers on the streets - everyone from the police to the forest service - to ensure the vote is at least as peaceful as it was during Kenya's last election. With its combination of a large economy, vast disparities of wealth, and political instability, Kenya is also viewed as something of a bellwether.
"I feel good. I feel positive because we ran a positive campaign", Kenyatta said after casting his vote.
The voting process is running smoothly in many parts of the country, but some parts have experienced a few technical issues that caused delay in the process. He urged supporters to gather on Wednesday in a downtown park for what he predicted would be a celebration.
Were Raila to win, it would upend the political dominance of the Kikuyu ethnic group, which has supplied three of Kenya's four presidents since independence from Britain in 1963.
"I urge Kenyan leaders to reject violence and incitement; respect the will of the people; urge security forces to act professionally and neutrally; and work together no matter the outcome".
Editar Ochieng, a resident of the Nairobi slum Kibera, where clashes broke out in 2007, has sent her two daughters out of town for the duration of the elections.
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The Missouri Highway Patrol were looking for Ian McCarthy , 39, of Clinton as a person-of-interest in the fatal shooting. Michael married his wife Cresinda in 2015, becoming a stepfather to her two sons. "You know he was doing his job".
Okoth called for vigilance, saying it brings credibility to the elections.
"There have been no incidents so far", Mahama said.
Kenya's general elections kicked off on Tuesday, with almost 20 million eligible voters expected to cast their ballots at over 40,000 polling centers to elect public officials, including the president.
Six elections are now ongoing in the country; the presidency down to the local representatives and this may account for delays in the polls across the country which is due to end at 5:00 pm local time. First, the vice president's rural home was attacked by a machete-wielding intruder and a little more than a week before elections, the man in charge of Kenya's electronic voting system was murdered. Kenyatta won by a thin margin, with just over 50% of the vote; Odinga alleged vote-tampering and took his case to Kenya's highest court, which ruled in Kenyatta's favor by validating the results. "I am going home to open the business and wait for results".
The two dynasties have always been rivals, and Kenyans feel so strongly about the vote that ambulances have been ferrying bed-bound patients to polling stations.
Early voters went to the polls across the country at sunrise.
Last month, a top election official was found dead, his body showing signs of torture. Voting began officially at 6am and is expected to end at 5pm local time with results to be announced within seven days.
This edition of the general elections has been headlined by the presidential race rivalry between incumbent Uhuru Kenyatta of Jubilee Party and Raila Odinga of The National Super Alliance (NASA).
This year, a new biometric identification system was set up that requires voters to verify their identity and registration using a fingerprint reader that often needs several tries before it works.
Around 19 million voters, half of whom are under 35, have been registered.