Tens of million people around the world will watch the American presidential debate, which begins at 2am (Nigerian time), on CNN.
Republican candidate Donald Trump and Democratic candidate Hillary Clinton will square up with each other in the historic debate.
Polls show the two US presidential candidates running neck to neck, although a few have given Trump the edge in the November poll.
Presidential debates tend to make candidates win or lose polls in America. The two candidates are billed to meet debate twice again (after this Tuesday) before the November 8 election.