The 26-year-old Frenchman, who last year won the Fleche Wallonne and Clasica San Sebastian, beat Jakob Fuglsang (Astana) and Wout van Aert (Jumbo-Visma) after an uphill sprint finish at the end of a 184km ride in and around Siena peppered with gravelled road sections.
The Deceuninck-QuickStep rider followed Fuglsang’s attack in the penultimate gravelled section and perfectly timed his effort in the narrow streets of Siena to prevail in the Piazza Del Campo.
“I’m just so happy, my team did a great job today. I knew it was a good race for me,” Alaphilippe said,
It was Decunik-QuickStep's fourth consecutive win in the 2019 classics after they claimed the Het Nieuwsblad, Kuurne-Bruxelles-Kuurne and Le Samyn.
“Strade Bianche was my first big goal of the season," Alaphilippe said. "I started pretty well in South America but I wanted to win here. I was very motivated with a strong team.
"It wasn’t easy to be the favourite of a race I never took part in previously but I’m quite used to the pressure now and I handle the situation pretty well.
"I felt heavy legs in the finale and Jakob Fuglsang was fresher than me. I had to arrive with him at the bottom of the San Caterina. I’m super happy that I made it.
"A cycling season is not only about the Flèche Wallonne and the Tour de France for me. I needed something new to motivate me, and that was Strade Bianche.”
It was on Monteaparti, at 800 metres, the shortest gravel segment in the race, that the winning move took shape, when Fuglsang accelerated, joined only by Alaphilippe and Van Aert.
The trio traded turns until the steep Colle Pinzuto, where Van Aert was dropped, leaving at the front only Alaphilippe and Fuglsang, who traded turns to open a one-minute gap over the main chasing group.
Just before Via Esterna di Fontebranda, on the outskirts of Siena, Van Aert bridged back to the leading duo, but only for a brief moment, as he was again dropped.
On Via Santa Caterina, Fuglsang tried to drop Alaphilippe, but he was up to the task in matching his opponent before rising out of the saddle for an explosive attack on the 16 per cent gradients and dispatching his opponent.
Alaphilippe is with Tour de France podium finishers Thibaut Pinot and Romain Bardet, one of France’s top riders.
Last year, he ended world champion Alejandro Valverde’s four-year reign at the Fleche Wallonne and he is now hungry for more.
“I want to win every race that I start with a winning chance,” Alaphilippe said.