Ben Carson at a September campaign rally in Cincinnati. (John Minchillo/AP)

Republican presidential candidate Ben Carson raised $20 million during the third fundraising quarter, a staggering amount for the self-professed Washington outsider that not only places him at the front of the GOP fundraising pack but also puts a spotlight on his strong support among the grass roots.

Sixty percent of the contributions to the retired neurosurgeon's campaign came from small-dollar donors who gave less than $200, according to a filing released by the Federal Election Commission on Thursday, accounting for nearly $12.5 million of Carson's total quarterly haul.

His campaign's strong fundraising numbers were undoubtedly bolstered by the strong anti-Washington sentiment across the country that has fueled interest in outsider candidates such as business mogul Donald Trump and former Hewlett-Packard chief executive Carly Fiorina among GOP voters. Trump and Carson lead the primary field in national polls, landing significantly ahead of establishment-friendly candidates such as former Florida governor Jeb Bush and Sen. Marco Rubio, also of Florida.

But while Trump's multibillion-dollar wealth insulates him from the typically grueling fundraising pressures faced by other candidates, one of the Carson campaign's key goals has been to transform the grass-roots energy he is seeing across the country into campaign contributions.

Thursday's financial disclosures show that the GOP firebrand's central message, which rests on his lack of political experience and his status as a Washington outsider, is resonating. In total, 402,000 individual donors made approximately 700,000 contributions, according to the campaign.

A dive into the campaign's expenditures shows that it has prioritized spending on fundraising operations intended to yield more revenue. Carson's fundraising expenses last quarter totaled $11 million, according to the campaign, while its operational expenses constituted $3 million of its total spending.

In total, the Carson campaign spent $14 million between July and September and ended the quarter with $11 million on hand. Of that, $9.5 million was spent on media and advertising. Nearly $2.7 million was spent on direct-mail expenses, while only $1.4 million was allocated for payroll expenses.

Carson has taken $31 million in contributions this year and has spent $20 million.

Bush was once expected to be the strongest fundraiser in the GOP primary, but a sluggish fundraising quarter called into question whether his “shock and awe” campaign is sustainable without stronger support from the base. The former governor raised just $13.4 million during the third quarter -- of which he spent $11.5 million -- and ended the period with $10.3 million on hand.

Read more:

[No more ‘shock and awe’: Jeb Bush now just another presidential aspirant.]

[Ben Carson, riding a fresh surge in the polls, braces for his close-up.]