The Italian was part of a small group of top riders heading into the final kilometres of the race, but – just as on Saturday's Giro dell'Emilia Donne – proved to be the strongest as she broke away to win on her own.
Veronica Ewers (EF Education-Tibco-SVB) continued her strong late-season form with a second place to follow up her runners-up spot on Saturday, while Ane Santesteban (BikeExchange-Jayco) rounded out the podium in third.
Longo Borghini now has six victories on her palmarès in 2022, including big wins at the Paris-Roubaix Femmes and the Women's Tour.
"It was definitely a nice win, on a route that suited me well with a hard and hectic final circuit which served as a launchpad to get the solo win," Longo Borghini said later.
"I knew the Montello climb well, the decisive point the race, and I knew I could make the difference there. It was a challenging but fast circuit and I needed a few efforts to make the difference. I knew several fast riders who would have a chance to survive and the small gap I finished with is the proof. Sierra showed to be really competitive, she was my biggest concern at some point. I was confident, I tried few attacks in the final two laps, and then the final lap was the good one.
"I'm good in this finale of the season. The form is there and I think I'm having a boost of determination pushing me in these last races. Emilia on Saturday and today's Tre Valli Varesine are the proof.
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"For me it's a sort of revenge for some key events of my season that didn't go as I wanted, like the Tour de France and the Worlds. It's like a relief. I'm really facing every race with the desire to have fun on my bike, to compete and race to win. I'm really enjoying this moment."
The challenging but short 88.9km race took in four-and-a-half laps around a hilly circuit in Varese, with back-to-back climbs of the Casbeno and Montello the main difficulties of the day and the finish line coming between the two.
Breakaway riders during the early-morning race included Alice Gasparini (Isolmant-Premac-Vittoria) and Sophie Wright (UAE Team ADQ), but the final reckoning played out with a near-full peloton after a strong attack group was neutralised heading into the final 20km.
As the pace upped, the bunch got smaller and smaller and a smaller elite group of riders emerged, including Longo Borghini and her Trek-Segafredo teammate Elisa Balsamo.
A lead peloton of fewer than 20 riders led the way into the final 10km of the race before Longo Borghini set off on her solo attack. It was a powerful move and proved to be too much for her rivals, her advantage growing out to 30 seconds as she raced into the final 5km.
The Italian eventually soloed to the finish, well clear of the rest, for another victory on home ground.
Dani Ostanek is Senior News Writer at Cyclingnews, having joined in 2017 as a freelance contributor before being hired full-time. Her favourite races include the Paris-Roubaix, Tour de France Femmes, Tro-Bro Léon, and cycling's fourth Grand Tour, the Volta a Portugal.
