Quintana laid down an early marker for his Giro d'Italia and Tour de France double when he won the Tirreno-Adriatico stage race after holding on to his overall lead at the end of the final time trial.
Australian Dennis (BMC) prevailed in the 10.5km solo effort against the clock to finish second overall ahead of Thibaut Pinot (FDJ).
He is the first Australian to win a time trial at Tirreno-Adriatico and only the second Australian to make the final podium after Cadel Evans who won the race in 2011. Matt Goss (in 2013) was the last Australian stage winner.
“This is an important victory for me," Dennis said. "I was on the bus when Jos van Emden set the best time. I knew from the Eneco Tour last year that it would be a time of reference. He’s very competitive. He’s always a threat.
"I know from my performance at the Terminillo that I need to lose two or three kilos to close that minute gap I miss compared to the climbers. I’m probably not going to do that for the coming Giro d’Italia. It’s safer to take a slower step. I give myself four years for winning a Grand Tour.”
Quintana built his victory with a win in the main mountain stage that ended up the Terminillo pass, finished with a 25-second advantage over Dennis, with Pinot ending up 36 seconds off the pace.
“It was more difficult to win Tirreno-Adriatico two years ago when I had more rivals who were more experienced than I was,” Quintana said. “Now I’m stronger and smarter, and I had a better team this time around.
“I won more with my head than with my legs. I expected to finish the week of racing in a better shape than I had at the start and that’s the case.
“I can pursue my preparation for my goals, the Giro d’Italia and the Tour de France, as I’m happy with my condition.
“It’s impossible to establish a hierarchy of the favourites for the Giro now. Some riders have been in the shadows this week but they’ll be shining in May. The level will be very high so I’ll have to be at 100 per cent for winning."
World champion Peter Sagan (BORA-hansgrohe) , one of the top favourites for Saturday's Milan-San Remo classic, was nearly taken down when a lady with a dog walked on a pedestrian crossing just in front of him.
“I was lucky there wasn’t an incident with the lady who crossed the road with her dog," Sagan said. "It was funny really. I didn’t brake because I was in my time trial position. I saw her really late, so the only way to avoid her was to go off road. Today I was relaxed – it was a rest day for me and I just wanted to get to the finish safe.
"I didn’t brake because I was in my time trial position. I saw her really late, so the only way to avoid her was to go off road. Today I was relaxed, it was a rest day for me and I just wanted to get to the finish safe."