But the focused 29-year-old came back with a bang, punching the air as he finished the 54km Northallerton-Harrogate route in 1:05:05.35 - more than a minute quicker than young pretender Remco Evenepoel.
Obviously there has been a lot of talk since the Tour de France, but it was just really special to come here in the best possible shape and defend this title, to show I haven’t hung the bike up and that I’m still here to win and give more to the sport.
Devastating Dennis blitzes field to defend ITT world title in style
Having won last year’s junior time trial and road race at the UCI Road World Championships, Evenepoel’s silver saw the 19-year-old Belgian announce himself on the elite stage having skipped the U23 ITT.
Behind European champion Evenepoel was Filippo Ganna, who took home the bronze for Italy. Meanwhile, Briton Alex Dowsett was fifth behind Patrick Bevin.
Highlights: Dennis still the time-trial master as young pretender Evenepoel clinches silver
A total of 57 riders tackled the 54km route, and after GB’s John Archibald set the early benchmark of 1:08:16.28, team-mate Dowsett set a time of 1:07:07.12 for the final 24 to beat.
Only four riders would go on to better Dowsett’s time, with Evenepoel crossing the line ahead of Ganna and Bevin to sit at the top.
But he was quickly knocked off his perch by Dennis, who was in the green when crossing the first and then second checkpoint, and did not relent to finish 68 seconds faster than Evenepoel.
Campenaerts tackles hill on foot after needing second bike change in ITT
There was disappointment for Victor Campenaerts - who required two bike changes - and Primoz Roglic meanwhile, who finished 11th and 12th respectively.
Roglic did manage to share some of the limelight however, catching up with Dennis – having initially been overtaken – to cross the finish line at the same time as the world champion.
'I'm still here to win' - Dennis revels in perfect day in ITT after 'tough year'