With the race favourites eyeing one another, Kwiatkowski slipped away near the end to join a breakaway group of four riders and didn’t stop, staying ahead of the chasers on the final descent.
The 24-year-old Kwiatkowski had time to stop pedalling and lift his arms in celebration as he won the rainy 158.3-mile ride, that started in heavy fog, in six and a half hours.
“I was feeling right on the last lap,” Kwiatkowski said. “I was just going for the win and I tried to risk it because I saw that some of the riders were still calculating. I didn’t and I won. This is incredible.”
Simon Gerrans of Australia was second in a photo finish, one second behind Kwiatkowski. Spaniard Alejandro Valverde was third for the third year in a row.
Britain’s Ben Swift kept himself in contention for much of the race but the 26-year-old was unable to stay the course and wound up in a photo-finish for 12th place.
Switzerland’s Fabian Cancellara just pipped Swift into 11th.
Nicolas Roche came home in 26th place for Ireland.
Former Tour de France winner Chris Froome withdrew with less than three laps to go after falling behind the peloton.
The 14 laps of the 18.2-kilometer route on well-paved roads took riders by a Templar castle in the city of Ponferrada and through its hilly surroundings in northern Spain. The course featured two short climbs, but the trickiest part was its long descent back into the city because of the wet surface.
Just when the sun had started to shine after a rainy morning, Tour De France winner Vincenzo Nibali fell in a low-speed crash involving a handful of riders. The Italian appeared unhurt and was able to join the peloton, but he wasn’t able to battle for the win. An early group of four escapees opened up an advantage of almost 15 minutes, but it was slowly reeled in by a peloton led for a long stretch by the Polish team.
“I am really thankful for my mates for what they did at the beginning,” Kwiatkowski said. “We decided to continue riding and stay at the front. I said right from the start that there is no time to wait, we have to lead the peloton because that was our best chance.”
Germany’s Tony Martin, dethroned as time trial champion by Bradley Wiggins this week, tried a solo effort with three laps to go. He, too, was caught by a small group which then relented and let the rest catch up.
Seeing Kwiatkowski speed away, Joaquim Rodriguez attacked on the last climb to try to catch him. Nibali couldn’t keep up, but Valverde, Gerrans and Philippe Gilbert quickly joined in, forming a formidable pack of pursuers.
But even though Kwiatkowski never opened up a gap of more than nine seconds, it was enough time for him to pull off the surprise.
“I knew that it was possible to arrive in a smaller group, especially in the rain, because it was really risky,” Kwiatkowski said.
It was Valverde’s sixth medal in the event. The Spaniard now has two silvers and four bronzes, but he again came up short of winning an elusive gold.