MEXICO CITY/SINGAPORE (BLOOMBERG) - The Mexican peso rebounded from a record low, a sign investors may perceive Mrs Hillary Clinton is outperforming Mr Donald Trump in the first US presidential debate.

The currency rose 1.4 per cent to 19.5934 per US dollar as of 11.13am in Tokyo, the biggest gains worldwide, as Mrs Clinton and Mr Trump clashed over trade, the economy and race relations.

The peso had borne the brunt of investor anxiety about the November election, sinking to an all-time low of 19.9333 before the clash between the candidates began.

"The peso started the debate near its weakest levels but at least the first 30 minutes or so looks to have been taken as a Hillary win," said Mr Sean Callow, a senior currency strategist at Westpac Banking Corp in Sydney. "In forex markets, the most obvious trade to anticipate a Trump presidency is to short the peso."

The bounce provides a respite for a currency that has posted the worst performance among its major peers in the past month, fuelled by polls that showed Mr Trump gaining ground on Mrs Clinton.

It has lost about a third of its value in the past two years. While weak points in Mexico's economy and emerging-market jitters are also contributing to bearish sentiment, traders and analysts say the recent slump is tied to the ascendancy of Mr Trump, who has vowed to renegotiate the North American Free Trade Agreement if he wins.

"The stronger Hillary is, and the stronger the chance of her victory, the better for the peso," Mr Eduardo Suarez, a strategist at Bank of Nova Scotia in Toronto, said before the debate. He forecasts the peso will gain to 18.4 per US dollar by the middle of next year.

One-month implied volatility on the peso, a measure of the cost of protection against future price swings, rose to the highest since November 2011 in the lead-up to the debate. Net short positions on the peso jumped more to a record high in the week ending Sept 20, according to the Washington-based Commodity Futures Trading Commission. HSBC says the peso could fall to 22 per US dollar in the event of a Trump victory.

The currency has often declined when Mr Trump's odds improved, but tends not to gain as much on data favouring Mrs Clinton, according to Alejandro Padilla, a foreign-exchange strategist at Banorte-Ixe in Mexico City.

"A Trump victory went from being a tail risk to being a real possibility, at least according to the polls," he said. "This is why the peso would depreciate significantly, as it was being used to hedge the elections."