In the kingdom's commercial capital of Jedda on Saturday, all the seven winning candidates were those whose names had appeared on what was dubbed the "golden list" - the pick of fundamentalist clerics.
Five of the six winners in Burayda, capital of the conservative al-Qassim province, similarly had been given a clerical nod, and the holy city of Madina also saw Islamist candidates doing well.
Many Islamists also won seats in the February and March municipal council polling elsewhere in the kingdom.
Though they will have significant sway on local political matters, the government can balance the councils by naming liberals to the half of all council seats reserved for government appointees.
Usama Aba al-Khail, head of the electoral committee, announced the results on Saturday in Jedda, one of the most liberal parts of the kingdom.
He did not provide winners' political or religious backgrounds. But the candidates, like the clerics, have made their views known.
"We are an Islamic country and we are Islamists. We will stick to our Islamic values in fulfilling our duties according to the book and al-Sunnah," said winning Jedda candidate Bassam Jamil al-Khadhr, referring to the holy Quran and sayings of Islam's founding Prophet Muhammad.
Al-Khadhr denied there was any coordination or formal list, which would have been illegal under Saudi election rules. However, the list of names was widely circulated on the internet and through mobile phone messages.
"We are an Islamic country and we are Islamists"
Bassam Jamil al-Khadhr,
"Of course, our respected scholars support us. We are people known for our public service. It is only natural that we will get such support," al-Khadhr said.
Municipal council posts have little power, but many Saudis jumped at the chance to have even a small voice in politics.
The Saudi monarchy, a long-time ally of Washington, has been under US pressure to make some democratic reforms.
But the limited experiment in democracy - only men could vote and run for seats on the half-appointed councils - also appeared to be an attempt to deflate the Islamic movement by bringing some Islamists into the system.
"We are religious people by nature and secular people are not accepted by the society"
Abd al-Rahman al-Yamani,
Abd al-Rahman al-Yamani, who secured the most votes in Jedda - nearly 12,000 of the 55,000 cast in the municipality - attributed the Islamists' success to popular support rather than a well-organised clerical campaign.
"We are religious people by nature and secular people are not accepted by the society," he said.
In Burayda, only one of the six winning council members was not among the clerics' recommendations - a businessman with strong tribal backing.
Thursday's voting was the last of three rounds, and also included the holy city of Makka as well as the northern areas of Hail, Tabuk and al-Jouf on the northern frontier with Iraq and Jordan.
A total of 244 seats were up for grabs on Thursday.
Nationwide, roughly half of the 1200 local council members are being elected.