Images showing thousands of people lining the streets in Arizona were widely shared by Republicans and the leader's core base.
But the photos were quickly debunked as fake. They actually showed an aerial view of crowds that had turned out for a championship parade for the Cleveland Cavaliers basketball team.
Official turnout figures from the Phoenix convention centre rally have not been released, but many have speculated they could be lower than expected.
Images posted to social media appeared to show Trump supporters filling just half of the room.
Mr Trump tweeted following the campaign event: "Thank you Arizona. Beautiful turnout of 15,000 in Phoenix tonight!"
— Matt McDermott (@mattmfm) August 23, 2017
— David Catanese (@davecatanese) August 23, 2017
Outside the rally, shouting matches and minor scuffles erupted between Trump supporters and some of the thousands of protesters gathered near the event.
Mr Trump had been discouraged from speaking in Arizona by local officials, with mayor Greg Stanton urging him to delay the visit in the wake of the Charlottesville violence. He claimed his president had "doused racial tensions with gasoline".
"With his planned visit to Phoenix, I fear the President may be looking to light a match," Mayor Stanton wrote. "That’s why I asked the President to delay his visit. It’s time to let cooler heads prevail and begin the healing process."
The former real estate mogul provoked a national furore in the wake of the Virginia protest organised by white supremacists - that led to the killing of a counter-protester - after he blamed the violence on "both sides".
The Phoenix rally saw Mr Trump blast the "dishonest media" for misrepresenting his remarks in a rambling speech designed to recapture the fervour that sent him to the White House.
Mr Trump's job approval rating dropped to 34 per cent in the wake of the violence, and is now at 35 per cent, according to the latest Gallup poll.