The 24-year-old Californian was second wheel on the final corner, just 250 metres from the line and won the uphill sprint ahead of Arlenis Sierra (Astana) and Cecilie Ludwig (Cervélo-Bigla).
Rivera had been part of a large group which came together on the descent of the final climb, within the closing 7km. It was just the fourth time in more than 40 editions the race has been decided by a large group sprinting for the win.
The result is the most notable result of the American’s career and comes after she joined the Dutch registered team over the winter.
The early part of the 131km race was animated by the home teams, with Anna Trevisi (Alé-Cipollini) attacking with Silvia Valsecchi (BePink Cogeas) and Simona Frapporti (Hitec Products), Building a gap in excess of 30 seconds.
When the trio were caught with less than 40km ridden, Anna Stricker (BTC City Ljubljana) and Latvian rider Lija Laizane (Aromitalia-Vaiano) also managed to establish a similar gap. However, when the latter was caught on the race’s main climb to the small village of Orino, Stricker was soon absorbed.
The event winds its way through the wooded hills of Lombardy, north of Milan, crossing the finish line in the small town of Cittiglio four times. Each of those laps contains the climb to Orino, which has often been the scene of the race winning move.
Repeated attacks on the climb by the likes of Jessica Allen, whose Orica-Scott team are based nearby, and her Australian compatriot Tiffany Cromwell (Canyon-SRAM) animated the race and whittled down the peloton, but failed to create a decisive selection and a large group was together to contest the final 17km lap.
For a few short kilometres on the final climb Australian champion Katrin Garfoot (Orica-Scott), Kasia Niewiadoma (WM3 Energie) and local favourite Elisa Longo-Borghini (Wiggle High5) pulled out a lead, though as the group crested the summit they were caught, leaving around 30 riders to contest the final.
Th top British rider was Dani King (Cylance) who finished 15th, one place better than her Strade Bianche result.
Lizzie Deignan (Boels-Dolmans), who won the two previous editions of the race, finished in 39th place.
The fourth round of the Women’s WorldTour, Ghent-Wevelgem, takes place next Sunday.
Trofeo Alfredo Binda Commune Cittiglio (131.3km)
1. Coryn Rivera (USA) Team Sunweb, in 3-25-26
2. Arlenis Sierra (Cub) Astana Women’s Team
3. Cecilie Uttrup Ludwig (Den) Cervélo-Bigla
4. Chantal Blaak (Ned) Boels-Dolmans, at 0-02
5. Elena Cecchini (Ita) Canyon-SRAM
6. Eugenia Bujak (Pol) BTC City Ljubljana
7. Elisa Longo-Borghini (Ita) Wiggle-High5
8. Ashleigh Moolman-Pasio (RSA) Cervélo-Bigla)
9. Katrin Garfoot (Aus) Orica-Scott
10. Rasa Leleivyte (Lit) Aromaitalia Vaiano, all same time