SINGAPORE, Sept 30 (Reuters) - Republican President Donald Trump and Democratic rival Joe Biden sparred on stage for the first time on Tuesday in a pivotal debate ahead of the Nov.3 U.S. presidential election.

With more than a million Americans already casting early ballots, the debates kick off as investors worry about prolonged uncertainty after Trump's refusal to commit to accepting the election outcome.

S&P 500 index futures lifted 0.6% during the debate as both candidates landed blows in early exchanges.

Here are analysts' reactions: AYAKO SERA, MARKET STRATEGIST, SUMITOMO MITSUI TRUST BANK, TOKYO "Right now it looks like an even split between Trump and Biden, so it is difficult for the markets to move. What people are most concerned about is the fairness of the election and how it will be carried out.

"There is still a lot of uncertainty, so it is difficult to see a clear trend for the dollar/yen. Under normal circumstances, the positive economic data from China we've seen would support risk-off trades, but this time is different." (Reporting by Stanley White in Tokyo Compiled by Vidya Ranganathan; Editing by Muralikumar Anantharaman)