Having enjoyed a three-minute lead on the chasing group with 20 kilometres to go, the Alpecin-Fenix leader was nearly mowed down by a late surge from Tour de France winner Tadej Pogačar (UAE Team Emirates) that whittled his advantage to just 10 seconds at the finish.
A shivering Van der Poel described the torture that he endured in the final kilometres.
"I was good until the last lap when I was completely empty. I don't even know how I got to the finish line today," Van der Poel admitted.
"The last 10-15 kilometres were really hell for me today. I thought he was going to get me. I couldn't ride 200 watts anymore, I was completely empty with the cold and the long solo I did. I thought he was going to get me and I'm really happy to be rewarded with the win.
"If I had finished second, it would have been a big disappointment. Did I make history? No idea. It feels like that to me, because I can't remember a race where I felt that way at the end. I was just dead in the end. I'm glad I won, but I was really dead."
The Alpecin-Fenix rider put in a long-range attack on the punchy Castelfidardo circuit as a cold front moved in and dropped the previously comfortable spring weather conditions into the single digits with strong winds and rain.
While riders like Egan Bernal (Ineos Grenadiers) were at the back of the group trying to bundle up against the weather, Van der Poel, energy gel still in his mouth, found himself with a small advantage on the field and decided, even though there were more than 50 kilometres still to race, he would keep going because he was cold.
"I wanted to race from far as well on this lap. Initially, it was good because we were away with 20 good riders, but they didn't work well together. And suddenly I was off in a descent while eating something. At that point, I felt really good so I decided to keep going. Only in the last 15 kilometres did I get really difficult. There was also a lot of wind to ride along here and it was extremely cold.
"I was too cold to put something on, I didn't expect it to be so cold, it was quite good actually at the beginning of the race," he said.
We've seen Van der Poel collapse onto the tarmac after winning Strade Bianche and the Amstel Gold Race, but the effort on the 205km stage pushed even the cyclo-cross World Champion to his limit, and we're not likely to see him doing any more attacking in the final stages as he looks to recover and hone his form for next weekend's Milan-San Remo.
"The body was empty. It was certainly one of the toughest days of my career," Van der Poel said. "I am certainly proud and also very happy that it worked out, because I had very little time left on Tadej."
When asked if such an extreme effort would pose a problem for Milan-San Remo, Van der Poel said: "I hope not. It's another week so I think I'll be back. I try to take it as easy as possible now. The time trial is not a goal for me and tomorrow there should be a sprint stage where I can try to save some energy."
Last year, Van der Poel struggled in the extreme heat of the August edition of Milan-San Remo but looks on form to challenge for his second Monument victory.
"I think the most important thing is the legs. Last year I just didn't have the legs to go with Wout and Alaphilippe. I hope to have the legs this year."
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