The speech was vintage Clinton - overlong for sure, insults delivered with a folksy grin, references to his own time in office and to his wife, Hillary - all designed to improve Obama's chances for reelection in an era of painfully slow economic growth and 8.3 percent unemployment.
The convention hall rocked with delegates' applause and cheers as Clinton strode onstage to sounds of "Don't Stop Thinking About Tomorrow," his 1992 campaign theme song.
"I want to nominate a man who is cool on the outside but who burns for America on the inside," Clinton said.
He sought to rebut every major criticism Republicans leveled against Obama at their convention last week in Tampa and accused Republicans of proposing "the same old policies that got us into trouble in the first place" and led to a near financial meltdown.
Those, he said, include efforts to provide "tax cuts for higher-income Americans, more money for defense than the Pentagon wants, and ... deep cuts on programs that help the middle class and poor children."
"As another president once said, 'There they go again,' " he said, quoting Ronald Reagan, who often uttered the remark as a rebuke to Democrats.
"In Tampa the Republican argument against the president's reelection was pretty simple: 'We left him a total mess, he hasn't finished cleaning it up yet, so fire him and put us back in,' " Clinton said.
Obama's high command had released excerpts of Clinton's remarks hours before his appearance as they worked to control the political fallout from an embarrassing retreat on the party platform.
Under criticism from challenger Mitt Romney, they rewrote the day-old document to restore a reference to God and to declare that Jerusalem "is and will remain the capital of Israel" - both of which had been in the 2008 platform.
Some delegates objected loudly, but Los Angeles Mayor Antonio Villaraigosa, presiding in the largely empty hall, ruled them outvoted. White House aides said Obama had personally ordered the changes, but they did not disclose whether he had approved the earlier version.
The episode was an unwanted intrusion for Democratic officials, who scripted the evening to showcase Clinton.
Obama flew into his convention city earlier in the day and arrived in the hall for Clinton's speech, where he joined the former president onstage afterward in a made-for-television moment.
Aides earlier scrapped plans for the president to speak Thursday night to a huge crowd in a 74,000-seat football stadium, citing the threat of bad weather in a city that has been pelted by downpours in recent days.
"We can't do anything about the rain. The important thing is the speech," said Washington Rey, a delegate from Sumter, S.C.
That and the eight-week general-election campaign about to begin between Obama and Republican challenger Romney, who spent his second straight day in Vermont preparing for this fall's debates with Obama.
Clinton shared prime time with Elizabeth Warren, the Democratic candidate for a Republican-held Senate seat in Romney's Massachusetts. For many years "our middle class has been chipped, squeezed, and hammered," she said.
Democrats signaled unmistakable concern about the growing financial disadvantage they confront. Officials said Chicago Mayor Rahm Emanuel, who was Obama's first White House chief of staff, was resigning as national cochair of the president's campaign to help raise money for a super PAC that supports the his reelection.
Unlike candidates, outside groups can solicit donations of unlimited size from donors. At the same time, federal law bars coordination with the campaigns.
Inside the hall, speakers praised Obama, but many went relatively easy on Romney after a series of scathing speeches on the convention's opening night.
Rep. Chris Van Hollen of Maryland, who sits opposite Republican vice presidential candidate Paul Ryan on the House Budget Committee, was something of an exception.
"When President Clinton left office, America had projected surpluses of trillions of dollars over the next decade," he said. "Then came two wars, two huge tax cuts tilted to the wealthy, and a new entitlement. Republicans didn't pay for any of it. Paul Ryan voted for all of it."
Clinton's speech marked the seventh consecutive convention he has spoken to party delegates, and the latest twist in a relationship with Obama that has veered from frosty to friendly. The two men clashed in 2008, when Obama outran Hillary Rodham Clinton for the Democratic nomination.
Hillary Clinton, then a New York senator and now Obama's secretary of state, was in East Timor on Wednesday as the party met half a world away. She made a cameo appearance on the huge screens inside the Time Warner Cable Arena, though, turning up in a video that celebrated the 12 Democratic female senators currently in office.