CHICAGO — President Barack Obama defeated former Massachusetts Gov. Mitt Romney on Tuesday to secure a second term that he vowed to pursue with the same resolve that catapulted him to the White House four years ago.

Promising that the “best is yet to come,” Obama told exhilarated supporters early this morning that they have made him a better leader over the past four years and are sending him back to the White House “more determined, more inspired than ever.”

“Tonight, despite all the hardship we’ve been through, despite all the frustrations of Washington, I’ve never been more hopeful about out future,” Obama said during his victory speech at McCormick Place. “And I ask you to sustain that hope.”

Obama locked up more than 300 electoral votes, edging Romney by better-than-expected margins in most swing states and delivering a knockout punch in crucial Ohio.

Obama said he had called Romney to congratulate him on a hard-fought race and is “looking forward to sitting down” with his one-time foe to hash out the country’s problems.

At his Boston headquarters, Romney told crestfallen supporters that he hopes Obama will be “successful in guiding our nation” during his second term.

“I so wish that I had been able to fulfill your hopes to lead the country in a different direction, but the nation chose another leader. And so Ann and I join with you to earnestly pray for him and this great nation,” Romney said.

Although Obama’s victory speech echoed of the hope-and-change mantra that first launched him to political stardom, Tuesday’s watch party at McCormick Place was a far cry from 2008’s jubilant rally at Grant Park.

The ticketed event included several thousand Obama campaign volunteers, many of whom contributed above-and-beyond hours in the final days of the election season. Four years ago, an estimated 240,000 Obama faithful flooded Grant Park to hear the first black president declare victory.

Today, Obama was more than aware of how times have changed.

“As it has for more than two centuries, progress will come in fits and starts,” he said. “It’s not always a straight line. It’s not always a smooth path.”

At about 10:15 p.m., thousands of Obama supporters at the convention center began brimming with raucous applause as news outlets projected an Obama win in the battleground state of Ohio. Moments later, NBC News called the presidential contest for the incumbent.

“This happened because of you. Thank you,” Obama then tweeted, attaching a photo of him embracing first lady Michelle Obama. “Four more years,” the photo’s caption read.

Twitter quickly announced that Obama’s message was retweeted nearly 272,000 times in the next half hour, making it the most retweeted tweet ever.

Several hours later, Obama took the stage at McCormick Place to thunderous clapping and reminded attendees about the United States’ humble beginnings.

“Tonight, more than 200 years after a former colony won the right to determine its own destiny, the task of perfecting our union moves forward,” Obama said. “It moves forward because of you.”