(CNN) Three of Philippines President Rodrigo Duterte's children posted resounding victories in the country's midterm elections this week as voters responded to what was largely seen as a referendum on the controversial leader's first three years in office with a strong vote of support.

More than 18,000 government posts were up for grabs in Monday's midterms, which were marred by sporadic violence, accusations of vote-buying and faulty counting machines

In the President's hometown of Davao, incumbent Mayor Sara Duterte on Tuesday led her re-election race with 580,440 votes -- while her sole rival, independent candidate Jun Marcellones, only received 4,270, according to CNN Philippines.

She will serve alongside her brother, Sebastian Duterte, who ran unopposed for vice mayor.

Their older brother, former vice mayor Paolo Duterte, is also in pole position for a seat in the House of Representatives with 197,370 votes, well ahead of nearest rival Susan Uyanguren, on 5,135 votes.

And with 98% of the vote counted in key Senate seats, members of the ruling PDP-Laban party and affiliated senators had secured a sizable majority, according to the country's Commission on Elections.

Nine of the 12 Senate winners were either part of the two lists endorsed by the Duterte administration, while the other three were not official opposition candidates.

The ruling party's high-profile Senatorial candidates include Duterte's former special assistant Bong Go, former Philippines National Police chief Ronald dela Rosa -- who oversaw much of the President's bloody, protracted war against drugs -- and Imee Marcos, daughter of former dictator Ferdinand Marcos.

"It is unprecedented that no 'genuine' opposition candidate has won in an election in the Philippines (while) it is a formal democracy," Aries Arugay, an associate professor at the University of the Philippines-Diliman, told CNN.

Philippines President Rodrigo Duterte shows the ink on his finger after voting in his hometown of Davao City, where three of his children were on the ballot.

Arugay said the increased support for Duterte could lead to a long-proposed raft of constitutional changes, providing individual states more autonomy and shifting the balance of power away from the influential National Capital Region (NCR), otherwise known as Metro Manila.

"If this happens, the senators will have to think where they will place themselves under a new system of government. Maybe some would like to be state governors or maybe prime minister. In other words, a whole different political arena can determine their loyalty to Duterte," Arugay said.

The sweep was such that the Malacanang, the Philippines' Presidential Palace, assured the public that the Senate would remain independent.

"They have to support the President when the agenda of the President is for the good of the people and they will have to oppose it if they feel in their conscience that it (runs) counter to the interest of the nation," presidential spokesman Salvador Panelo said Tuesday.

Duterte has enjoyed high levels of support despite his divisive policies, with Philippine pollster Social Weather Stations reporting a 72% approval rating in early May.