The results were expected to be declared official later today.
Mr Keesin's Rak Patong party won 17 of the 18 seats contested to maintain his solid grip on Patong politics.
Mayor Pian, a force in local politics since 1994, won with 4352 votes. Rivan candidate Kittisan Kuru and his Patong Kawna (Patong Development) group attracted 3154 votes.
Phuket's Electoral Commission chief, Kittipong Teangkunakit, said that one of the key issues appeared to be polluted water in Patong.
''We can't determine how people voted but the turnout in areas where 'black water' has been an issue was exceptionally high,'' Khun Kittipong said today.
Mayor Pian, perhaps the strongest advocate of a tunnel through the Patong Hill to provide a speedier alternative to the hill road, is likely to take the vote as an endorsement of the tunnel project.
The total of Patong citizens who cast votes was 8143, or 63.46 percent of those eligible, quite a high figure in terms of Phuket, where voting is not compulsory.
For some who also voted in the island-wide Phuket Provincial Administrative Council elections the previous Sunday, it was the second weekend in a row they had had to go to the polls.
Thailand's election laws restrict the sale of alcohol from 6pm on the Saturday preceding a poll to midnight on Sunday.
Bars and night venues in Patong have had to forgo as much as 10 million baht in revenue over two weekends in support of democracy.
Critics of the high cost paid by Patong businesses and the effect on tourism have pointed out that there appears to be no valid reason why the elections could not have been held simultaneously.
Mayor Pian, 68, became Patong's first elected mayor in 1995 and, once the polls have been declared valid, will be beginning his fifth term in office.