In a lively and unusually civilized debate Wednesday, Democrat Barack Obama and Republican Mitt Romney clashed on who would be the better champion of the middle class – a match that provided high drama but no critical game-changers.

The former Massachusetts governor delivered a confident, often aggressive and energetic performance. It was among the best of his campaign and in clear contrast to the president, whose delivery was more muted, measured and, at times, meandering.

The first of three presidential debates offered Americans their first side-by-side comparison of Obama and Romney and came at a pivotal moment in the 2012 presidential race.

There are 33 days until the election, and early voting has begun in 34 states. Romney, who has slipped in recent swing-state polls, needed a breakout performance in the event, at the University of Denver.