The fight was interrupted early on as Stevens carried out a low blow to the groin that saw the Japanese need a five-minute break.
Evolve MMA's Aoki, who has yet to defend his lightweight belt after winning it at the previous One FC event in Singapore, managed to recuperate in time and secured a takedown before the end of the first minute.
Stevens, who had never been submitted in 16 fights, was wary of Aoki's submission attempts and adopted a full guard in a matter of seconds.
And although the Tiger Muay Thai fighter managed to reverse the position within the opening round, he was very much second-best within the encounter and appeared relieved when the bell signalled the end of the first five minutes.
Stevens was much more defensive in the second round and did his best to avoid Aoki's attempts to sweep him onto the floor but the Japanese was relentless in his resolve and got on top once more.
Try as he might, the former Dream champion just could not find an opening, though, and, halfway through the round, had to resort to grabbing both of Stevens' flailing legs in order to try and immobilise his opponent.
It failed to lead to anything substantial as Stevens kept squirming out of his opponent's control but the American did become the victim of an inadvertent knee just as he was getting up towards the end of the second round.
To make matters worse, Stevens also earned a yellow card for having aimed kicks at Aoki's spine when he tried to get out of a sticky situation.
Knowing that he was clearly losing out on the scorecards, Stevens was much more ambitious at the start of the final round, even carrying out a cartwheel kick which ultimately caused no trouble to his opponent.
Aoki waited until he could clinch Stevens instead through a single leg takedown at the 1:30 mark and took the fight to the floor, nullifying Stevens' approach of utilising his striking pedigree.
The Japanese man's eagerness to penetrate Stevens' guard did see him become the victim of a head-and-arm choke but the American could not make it count and instead saw Aoki climb onto his back for a rear-naked choke attempt in the dying seconds of the fight.
In the end, the contest came to a tepid end and the judges duly awarded Aoki the win for demonstrating greater intiative during the three rounds, improving the 30-year-old's record to an impressive 34-6-1.
Aoki's win also came shortly after team-mate Eddie Ng secured a victory of his own against Muay Fit's Peter Davis, courtesy of a verbal tapout following an armbar maneouvre at 1:46 in the first round.