President Barack Obama broke Mitt Romney's dominance of fundraising last month after sending out a series of increasingly desperate and frenetic appeals for cash.

Obama raised more than $114m compared with Romney's $111m, figures released on Monday showed. It comes after three straight months in which the president has been beaten by his White House rival in terms of campaign donations.

Obama's $114m in August represented a big jump from the $75m he raised in July, and came after a series of emails, television appeals and other pleas for help.

Jim Messina, Obama's campaign manager, attributed the rise to small donations. The Democrats like to portray their fundraising as being reliant on a large grassroots movement, rather than the wealthy donors they claim Romney relies on.

More than 1.1 million made contributions averaging $58, the campaign said. More than 317,000 had never contributed to a campaign before, it added.

The Obama camp said that since the re-election campaign began, more than 3.1 million Americans have donated money to their cause, more than in 2008. Ninety-eight percent of donations were $250 or less.

Obama's surprise fundraising success was announced earlier Monday in a tweet from his campaign team less than 30 minutes after the Romney campaign published its results.

In the message, the Obama campaign team included a caution: "No celebrating because they're going to have an even bigger September. But now we know we can match them, doing this our way."

In spite of Obama's success last month, he still faces being outspent overall. Romney has more money stashed away for the remainder of the campaign, about $169m, partly because he was unable to spend it until he formally became the Republican presidential nominee two weeks ago.

The Obama team has not disclosed how much it has in the bank, though it is substantially less, mainly because it spent around $120m in negative adverts in swing states over the summer attempting to define Romney as elitist, uncaring businessman.

Romney also enjoys a huge advantage from Super Pacs. These political action committees are legally separate from the campaign teams, but the distinction often appears to be more theoretical than practical.

The Super Pacs supporting Romney, such as Restore Our Future and Karl Rove's American Crossroads are easily outraising their much smaller Democratic equivalents, mainly through reaching out to rich business leaders.

Restore Our Future and American Crossroads between them have raised about $1 billion, and these are just two of many Republican Super Pacs.

The difference in Super Pac spending power could still mean that Obama, as his campaign team claims, will be outspent two to one in the remaining two months of the campaign.

At the Democratic convention in Charlotte last week, Chicago mayor and former White House chief of staff Rahm Emanuel was recruited to the main Obama Super Pac, Priorities USA, whose performance so far has been poor. A target has been set of raising £150m by election day.

The Obama campaign announced the August figure on Twitter, though all the details do not have to be released until it formally reports to the Federal Election Commission later this month.

Messina said: "The key to fighting back against the special interests writing limitless checks to support Mitt Romney is growing our donor base, and we did substantially in the month of August.

"Fueled by contributions from more than 1.1 million Americans donating an average of $58 — more than 317,000 who had never contributed to the campaign before — we raised a total of more than $114m. That is a critical downpayment on the organization we are building across the country — the largest grassroots campaign in history."

Romney's national finance chairman Spencer Zwick and the Republican national committee chairman Reince Priebus, said in a joint statement: "Mitt Romney and Paul Ryan are offering bold solutions to our country's problems. That is why we are seeing such tremendous support from donors across the country."