De Minaur battles to DC Open crown
Seventh seed De Minaur looked to be heading for defeat against his 12th-seeded Spanish opponent after trailing 5-2 in the deciding set in Washington.
But Davidovich Fokina -- chasing the first ATP title of his career after losing in three previous final appearances -- failed to capitalise on his hefty lead.
The Spaniard appeared to tighten when serving for the match at 5-3 up to allow De Minaur to claw it back to 5-4.
But Davidovich Fokina responded to that missed opportunity by then earning three match points on De Minaur's serve in the next game.
Yet once again, the Spaniard was unable to take advantage and De Minaur survived to hold serve and level the match at 5-5.
The next two games went on serve to set up the tie break and De Minaur was quickly in control, sealing victory on the first of three match points with an ace, to settle a 3hr 2mins slugfest.
De Minaur said he had never doubted his ability to turn around the final.
"I just kind of knew I could do it," De Minaur said in his on-court interview. "I just backed myself to commit no matter what, and if I lost this match, it was going to be on my terms.
"I've had a couple of brutal ones not go go my way, so I'm glad this one went my way," the 26-year-old from New South Wales said.
The win was another agonizing setback for Davidovich Fokina, who had already reached -- and lost -- two other finals this season.
The defeat echoed his loss in the final at Delray Beach in February, when he was unable to convert two match points before losing to Miomir Kecmanovic.
"Congratulations to Alex, he deserved the win," Davidovich Fokina said. "He was fighting for every ball. He always pushed me to my limits."