Obama remains ahead of former Massachusetts governor Mitt Romney 49-45% among voters nationwide, with a 56-38% lead among women, according to the Quinnipiac University poll.

Romney leads 52-42% among white voters and 53-42% among men, it found.

The poll came out a day before the first of three presidential debates, high-stake bouts that could offer Romney his last opportunity to reverse the momentum of the race, which has been against him for weeks.

The two candidates have long been running neck-and-neck in nationwide polls, but Obama has pulled ahead in many of the crucial battleground states that -- because of the US voting system -- are likely to decide the race.

Romney has reeled from a series of missteps in recent weeks -- including a fumbling response to the deadly attack on the US consulate in Libya and a video of remarks dismissing 47% of Americans as unmotivated government dependents.

The poll found that 54-28% of voters expect Obama to win Wednesday's debate, which could work in Romney's favor by raising expectations about the president's performance.

However, debates are only believed to have decided elections on rare occasions, further ratcheting up pressure on Romney to deliver.

Quinnipiac surveyed 1,912 likely voters nationwide from September 25-30 by phone, with a margin of error of 2.2 percent.