A back complaint forced feelgood story Reilly Opelka to retire in the first set of the final trailing 4-1.
It handed the Czech his second ATP singles trophy to follow last year's Adelaide International triumph.
Lehecka was then immediately back in action with countryman Jakub Mensik, the pair saving four match points in an enthralling 6-3 6-7 (7-2) 10-6 doubles final loss to British duo Julian Cash and Lloyd Glasspool.
Victory there would have meant Lehecka was the first to win both events at an ATP tournament since Australian Jordan Thompson in Mexico last February.
Opelka missed nearly two years on tour after wrist and hip injuries but, having returned in July, had charmed the Pat Rafter Arena crowds on a run to the final that included taking the scalp of Novak Djokovic.
A lingering back injury got the better of the American giant on Sunday though, with Opelka unable to move or serve with fluency from the outset.
"Thank you and sorry at the same time," the 211cm Opelka said.
"It's been a great week for me ... got a lot of great matches in here.
"The tournament doctors and physician were unbelievable. They threw the kitchen sink at it all day but it wasn't right to compete."
Before his injury, Reilly Opelka's efforts in Brisbane included a win over Novak Djokovic. (Darren England/AAP PHOTOS)
Opelka had treatment on his wrist in Saturday's semi-final win and the former world No.17 is still confident of playing at the Australian Open from Sunday.
World No.28 Lehecka, who beat third seed Holger Rune in the first round, progressed to the final after defending champion Grigor Dimitrov retired from their semi-final on Saturday citing hip pain.
"I know how you feel, Reilly. It's been an honour to see you back on tour," Lehecka, who will defend his Adelaide title this week, said.
"It was a great week here for me in Brisbane. I just love to play here in Australia."
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