Despite being sidelined for seven weeks by an early-season concussion, Guarnier began September’s World Championships road race as one of the favourites. Hiding near the front of the peloton, with over half the 158km race behind her, she had been invisible. However, the moment she crashed descending Bergen’s Salmon Hill, she knew her challenge for the world title was over.
"I immediately got on the radio and said 'It's Megan, I crashed, and I broke my jaw'," Guarnier told Cyclingnews. “Then I realised what I said, and I thought, 'you're talking, you can't talk well, but you're talking, it's just a broken tooth that's why you can't close your mouth.
"I was trying to rationalise it. I didn't want to get in the ambulance because that was the end of my race. I had a trip planned with my Mom to Rome, and I thought if I get into this ambulance this is all over. But the doctor looked at me, and I guess it was kind of hanging there."
The break and displacement were one of the worst her doctors had seen, and she continues to suffer from the injury five months later. Chewing food is not easy, she wears a mouth guard at night to deal with spasms, and just pushing her lower jaw forward is a success. She admits, however, it could easily have been much worse.
"I'm lucky it wasn't my head again, and I'm lucky I didn't break both sides, and I'm lucky I still have my teeth. What was worst about it was I came in after a tough start to the season, building back up, getting my fitness and I hit everything perfect for that day.
"It is such a strange injury, but it hasn't affected my training and it hasn't affected my motivation."
The accident was a bitter blow, especially after fighting her way back from the concussion she suffered at Spar Omloop van het Hageland in late February. It caused her to withdraw from Strade Bianche the following weekend and ruined her spring. By the time she returned for the Ardennes Classics - races that suit Guarnier - her earlier form was gone.
Stage wins in California, Norway and the final stage at the Giro Rosa were the year's silver linings and, ever the optimist, Guarnier refuses to see 2017 in a negative light.
"I still won races; I still had a good season, I kept my focus, and got to where I needed to be," she said. "I have been fortunate in my career not to have bad years and every year has been a progression, I would still call last year a progression, but I did not get to display it because of injury."
Her tally of three Women's WorldTour wins would be the envy of many in the peloton, but is put firmly in the shadow of her 2016. That year, general classification victories at the Giro Rosa and Amgen Tour of California, along with success at the now defunct Philadelphia International Cycling Classic saw Guarnier top the UCI ranking and win the inaugural Women's WordTour. The contrast between those two seasons forms part of the reason she will be more circumspect in her 2018 campaign.
"I don't have any big overarching goals because coming off 2016, with that great year, and then having the next year as it was, I just want to have fun this year.
"Of course, I always look to the spring Classics as I love those races, I love Strade [Bianche], I love the Ardennes Classics, Flanders is super special, so those are always races that I love participating. If I get a result that is the icing on the cake this year. And of course, the Giro is always a favourite."
Having returned to the US after a European team camp, Guarnier will begin her season on March 3rd at Strade Bianche, a race she won in 2015.