The National Front coalition defeated the opposition Islamic party to retain a legislature seat in its stronghold in southern Johor state by a wider margin than in general elections in 2008, the Election Commission said.The by-election, called after the death of the incumbent, didn't change the balance of power in the state assembly but was seen as a barometer of Najib's popularity.The victory came just three months after two other by-election wins by the National Front, which has battled to regain public support after clinging to power despite losing more than one-third of the seats in Parliament in the 2008 polls.The Islamic party is part of a three-member opposition alliance led by former Deputy Prime Minister Anwar Ibrahim which made major inroads in 2008 but saw its fortunes reverse in recent months amid infighting.Malaysia's next general elections are not due until mid 2013, but analysts say Najib could call for early polls this year to take advantage of the opposition disarray and a strong economy."Najib has every incentive to call general elections. The momentum is there," said James Chin, a political science lecturer at Monash University in Malaysia.Sunday's by-election was marred by heavy rain that caused flash floods in the area, forcing more than 800 residents to be evacuated and resulting in a lower-than-expected turnout.