Thanks to the self-sacrificing efforts of Longo Borghini in the final two kilometers, Deignan could follow wheels and wait, saving her energy until the last few hundred meters where she was able to come around two-time winner Marianne Vos (CCC-Liv).
"It's phenomenal! Sometimes when you're training hard and things aren't going your way, it's frustrating," said Deignan. "Finally it seems like the luck is on our side. To be part of Trek-Segafredo is the best feeling - this is a team victory!"
During the race, the entire team's work, and Longo Borghini's display of camaraderie in the closing kilometers, gave goosebumps.
The battle for the win was between the six strongest women in the race, the select group created after World Champion Annemiek van Vleuten's (Mitchelton-Scott) pushed a fierce pace on a climb 45 kilometers from the end.
Trek-Segafredo was the only team with two in the group, and it made the difference.
Longo-Borghini's first attack came with just over two kilometers remaining, and Vos chased, pulling the group back to the Italian's wheel. Immediately, van Vleuten countered. Vos chased again.
Longo Borghini fought hard to stay in contact with the group and, without hesitation, jumped again at 1700 meters to go. For a second time, the group chased and caught her back. This time, Longo Borghini stayed on the front and pulled the group, hoping to keep the pace high and thwart off any more attacks.
But under the one kilometer to go banner, van Vleuten accelerated hard. The four others were quickly on her wheel, but a tired Longo Borghini fell behind.
At 700 meters to go, the pace slowed. The five began to eye each other. It was all Longo Borghini needed. Refusing to give up, once again she clawed back to the group and, with one last immense effort, came around and drove for the line.
Vos had no choice. She jumped after the Italian and started her sprint earlier than expected. Deignan followed, grabbing enough of the Dutch woman's slipstream to just come around her at the line.
A thrilling finish. And seamless solidarity between the Trek-Segafredo teammates.
"I was just relieved that I won it. What a performance by Trek-Segafredo today! Every single rider played their part and me and Elisa just really had to wait for final," said Deignan, heaping praise on the team. "Elisa did the perfect job, and forced Marianne to sprint early, and I took advantage of that.
"I think I had two of the best sprinters in the world in the car, [Team directors and former riders] Ina-Yoko Teutenberg and Giorgia Bronzini have both beaten Marianne Vos in lots of sprints, so I had the best advice and their advice was 'patience' and I took it."
Deignan's second victory in five days after winning GP de Plouay (August 25) gave the Briton the lead in the UCI Women's WorldTour ranking. "That's a nice surprise!" added Deignan. "I look forward to wearing [the leader's jersey], it's always an honor."