Rocked with a big right hand from Roman, McDonnell then struggled to cover up as the American piled on the pressure until the Doncaster fighter touched down.
Though McDonnell made the count, the referee Mark NelsonÂ waved off the fight, giving Roman a third successful defence of his WBA title at Chicago's Wintrust Arena.
It had been an exceptionally valiant performance from McDonnellÂ in his second attempt at a world title.
He will board his flight home having done what he did in his first challenge '“Â impress against elite opposition that is arguably a level above.
The nearly man once again.
Though champion Roman had the better of the first half of the fight, McDonnell grew into the contest and was enjoying the better of the work in the later stages with his ever-superb engine driving him on.
It proved to be a clash between workrate and slickness, with Roman providing the latter and ultimately delivering the big telling moment inside the final 30 seconds of the tenth round.
Both men settled into the fight quickly with Los Angeles fighter Roman showcasing his fast hands as landed a couple of eye-catching right hooks to body and head.
McDonnell landed some good shots himself but his best work came from his movement, weaving away from shots.
And that workrate saw him arguably edge the second, seeing him throwing plenty of shots to out-work Roman, who nevertheless landed meaningful efforts in short bursts.
The early rounds were back and forth and Roman took the third, again connecting with the more telling blows, particularly from his sharp right hand.
But McDonnell's busyness in the fourth earned him the round. Working off the jab and using his four inch height advantage, he landed plenty in a quieter round from the home fighter.
Roman however began to put a stranglehold on the bout in the middle rounds. Though always close, his was the better work with snappy shots thrown in bursts.
McDonnell's movement continued to be excellent but he was struggling to keep Roman out.
The champion enjoyed his best three minutes in the sixth, showing real explosiveness with strong counterpunching and stringing together shots.
After another strong round in the seventh from Roman, McDonnell responded superb to suggest he was far from finished.
In the eighth he took most of the shots on his gloves and worked superbly, peppering Roman with jabs and following up with a series of excellent right hands to the body.
And he continued his work in the ninth, moving in and out of range in slick fashion and delivering much the better of the work.
But one shot in the tenth would ultimately determine the outcome.
McDonnell spun straight onto a big right hand from Roman and was immediately in trouble.
Roman spotted the opening and unleashed a barrage of shots, landing repeatedly with the upper cut until McDonnell touched down close to the ropes.
Though he rose to his feet, referee Nelson was not satisfied and waved off his brave title challenge, condemning McDonnell to only the second defeat of his career.