Rhodes' dreams of becoming the youngest post-war British world champion were shattered by the Canadian Otis Grant, whose experienced display of controlled, efficient boxing earned him a unanimous points win.
"I'll be back, which is the main thing," Rhodes said. "I will be world champion - I'm only 21. I thought I boxed well and got my second wind around the sixth or seventh."
It was undoubtedly Rhodes' inexperience when compared with the 31-year- old which told in the end. Grant, a veteran of 31 professional fights, had controversially drawn with then champion, Lonnie Bradley, in a previous challenge for this title in March, only for Bradley's enforced retirement because of an eye injury to give him chance.
He was impressively economical in his approach, controlling the centre of the ring, picking off Rhodes regularly with left hooks.
The new champion paid tribute to Rhodes' stamina. Grant, who has a day job teaching disadvantaged children in Montreal, said: "I know he needed the last round so I had to be careful and not get caught by anything stupid. He has nothing to be ashamed of."
Rhodes will now take a break before easing his way back into the title picture, but the inevitable talk of a re-match was not ruled out by his promoter, Frank Warren. "I think we can make the return some time next year," Warren said. "I was impressed with the things Ryan did but there are also things he can sharpen up on."
Rhodes' trainer, Brendan Ingle, added: "It was a great performance. He's just gone in with a world-rated fighter."
l - Mark Staniforth