The Australian government on Saturday won a crucial by-election that restores its tenuous grip on power that was threatened by a constitutional ban on dual citizens sitting in Parliament.

The conservative Liberal Party candidate John Alexander regained his Sydney electorate, defeating Kristina Keneally, the Las Vegas-born candidate for the center-left Labor Party who was once leader of the New South Wales state government.

Alexander had been forced to quit over a constitutional ban of dual citizens sitting in Parliament. The former champion tennis player was able to re-contest the electorate he had held since 2010 because he renounced the citizenship he inherited from his British-born father.

The by-election returns Prime Minister Malcolm Turnbull's government to the single-seat majority it held in October when the High Court created a constitutional crisis by ruling that five lawmakers were ineligible to sit in Parliament.

They included Deputy Prime Minister Barnaby Joyce, who was able to successfully contest a by-election on Dec. 2 because he had renounced the New Zealand citizenship he inherited from his father.

Alexander was regarded as the favorite to win the by-election. But the government had feared that voters would take the opportunity to punish the ruling coalition, which has trailed Labor in most opinion polls since the last election in mid-2016.

This year, nine lawmakers lost their jobs for contravening a unique Australian constitutional quirk that demands lawmakers must be solely Australian citizens.

But only two so far have been members of the House of Representatives, where parties need a majority to form a government. The remainder have been senators, who are usually replaced by members of the same party without new elections.

Several more by-elections could further shift the balance of political power next year, with more government and opposition lawmakers facing questions over whether they were still dual citizens or whether they had renounced a second citizenship in time to legitimately nominate for the 2016 election.

Many question whether the ban on dual nationals in Parliament is appropriate for a migrant nation where almost half the population was born overseas or has a migrant parent.