Michelle Obama has strongly pitched for another innings for her husband at the Democratic Party Convention.

Conceding that change is a slow process, the US first lady asked voters to give Obama a chance to carry on the change he initiated four years ago. Change was Obama's successful poll plank in 2008.

"He [Barack Obama] reminds me that we are playing a long game here, and that change is hard, and change is slow, and it never happens all at once. But eventually we get there. We always do," Michelle told the national convention in Charlotte, North Carolina.

The first session of the convention also witnessed scores of governors and mayors campaigning for Obama. The convention will see former president Bill Clinton campaigning for the Democrats and later President Obama will also address the gathering.

Michelle's speech contained a blend of subtle jibes at Republican opponent Mitt Romney and his wife Ann Romney without directly mentioning their names.

"For Barack, success isn't about how much money you make, it's about the difference you make in people's lives. He was the guy whose proudest possession was a coffee table he'd found in a dumpster, and whose only pair of decent shoes was a half size too small," Michelle said, taking a dig at Ann.

Michelle went on: "He [Obama] believes that women are more than capable of making our own choices about our bodies and our health care. That's what my husband stands for. We learned about honesty and integrity. That the truth matters. That you don't take shortcuts or play by your own set of rules, and success doesn't count unless you earn it fair and square."

During her passionate speech, she provided a personal touch about her husband portraying him as a loving family man.

The Democratic convention has come at a crucial time as they are fighting to steal the spotlight from the Republicans who held their national convention a week ago in Tampa. An opinion poll gave Obama a wafer thin lead over Romney.

With presidential elections on the cards in November 2012, both Obama and the republican hopeful are trying to capitalise every opportunity over the coming weeks.

The presidential candidates will also been debating in the coming weeks where Obama is likely face tough questions on economic policies.