MANILA - Sen. Ferdinand "Bongbong" Marcos Jr. threatened legal action Saturday to reverse his narrow defeat to incoming vice-president Leni Robredo, which analysts said had been his family's best chance to regain the presidency.

The only son and namesake of the late dictator, Ferdinand Marcos, had aimed for the family's biggest political victory since its humiliating downfall in 1986 after a "People Power" uprising ended 20 years of the family's rule.

An official canvass showed Friday that Marcos, 58, lost the vice presidential contest to neophyte rival Robredo by just over 263,000 votes.

Tough-talking Davao City Mayor Rodrigo Duterte won the separate presidential contest by landslide.

But Marcos insisted Saturday he was potentially deprived of nearly four million votes through cheating and malfunctioning vote-counting machines, and was gathering evidence for a potential "election protest".

"The search for Senator Marcos's missing votes did not end with the canvassing," his lawyer George Garcia said in a statement Saturday.

Any legal action would be made only after Robredo is proclaimed the official winner, Garcia added.

The Marcos family had targeted the vice presidential post as a route back to the Malacanang palace through a subsequent presidential run for the son in 2022.

"I think this election was arguably the best and probably last chance for the Marcoses to wrest back control of Malacanang," De La Salle University international affairs and political science professor Richard Javad Heydarian told AFP.

"Six years down the road, (the) Marcoses could face a very different zeitgeist with the shadow of defeat hanging over their shoulders," Heydarian added.

"It (the loss) would make it that much harder for the Marcoses to regain power through elections," Ramon Casiple, executive director of the Institute for Economic and Political Reforms in Manila, told AFP.

Barring a reversal of the May 9 result, Marcos would have to wait for the 2019 mid-term elections to try and regain his senate seat, Casiple added.

The Marcos family fled to US exile after the bloodless revolution ended the dictator's one-man rule, in which thousands of critics were thrown in prison and $10 billion was allegedly plundered from state coffers.

The patriarch died in exile in Hawaii in 1989, but no member of the family ever served in jail for the alleged crimes.

Despite the loss, analysts are not ruling out his son's potential presidential run at the end of Duterte's term in 2022.

Heydarian and Louie Checa Montemar, a De La Salle development studies lecturer, both said the Marcos family would remain a major force, at least in its traditional bailiwick of Ilocos Norte province but also as a presidential contender.

"The only way now to banish any immediate future threat of a Marcos comeback would be to live up to the promise of raising the (economic prospects of the) marginalized," Montemar told AFP.

This month the dictator's widow, Imelda Marcos, swept to a third term in the House of Representatives representing Ilocos Norte province, while their daughter Imee Marcos became provincial governor for the third straight time.