Dennis was hoping to finish off a difficult season with a medal result in Doha but ran out of gas after a solid start to the 40km time trial.
"I didn't have it today," Dennis said. "My power was 30 watts less than what I did on Sunday [in team time trial]. It's been a long season."
Contrasting Dennis's performance was race winner Tony Martin (GER), who rode faster that nine of the six-rider teams from that same race.
Dennis was the third to last of the 66 starters and looked strong at the first intermediate checkpoint after 13.6 kilometres, with the fifth fastest time.
By the second checkpoint, Dennis was fourth fastest, but 35 seconds behind Martin. He then finished in a time of 46min and 10.11sec, enough for fifth and later sixth when all riders finally completed the course.
But the real story was written on the clock, he had faded between the second time check and finish - from 35 seconds behind Martin to 1min 27sec.
The post race deconstruction of Dennis's ride was left to national team selector and road director Brad McGee.
"We know if we put it all together, we could be legitimately on the podium if not winning this thing based on Rohan’s progression over the last 18-24 months," McGee said.
"But it just wasn't to be. From speaking to Rohan briefly, it was obvious from his analysis of his performance that he was missing that final 10 per cent of his power.
"That was all that was missing. His delivery, his line, his pacing, it was all spot-on. He was missing that final cog down."
McGee identified Dennis's long season, which included the Rio 2016 Olympic Games as a factor in the result.
"It doesn't take much searching to realise that this result is the product of coming off the back of a long and arduous season, a huge campaign in Rio," McGee said.
"Rohan carried his form into the following races including Eneco Tour but evidently he hasn't been able to hold onto that wonderful form to Worlds."