The Italian national champion, who was second last year behind his team- mate Franco Ballerini and third in 1996 behind another team-mate, Belgian Johan Museeuw, this time took his own chance by breaking away 25 miles from the finish.
His victory in the 171-mile World Cup race, known as the "Hell of the North" and run yesterday in windy but dry conditions, was the fourth by a Mapei rider in five years.
It was also the third time Mapei had swept the podium places as Tafi's Belgian team-mates, Tom Steels and Wilfried Peeters, were second and third. The victory was all the sweeter for the 33-year-old from Florence because on two previous occasions he had been forced to sacrifice his chances to another rider. In 1996, he crossed the line in tears after the Mapei director, Patrick Lefevere, decided he should allow Museeuw to win. Last year, he worked hard to help Ballerini win his second victory.
This year, circumstances were on his side. Ballerini left to join Lampre at the end of last season and he was too isolated on Sunday to stand a chance.
Museeuw had a terrible crash in the gruelling Wallers-Armeberg "trench" last year and he decided not to take any risks this season and work for Tafi.
"This morning Lefevere told me it was my turn and the team did a great job for me," the Italian said. "Once again, Mapei showed we were a great team."
It was at the end of the infamous trench - a long cobbled climb lined by deep ruts in the middle of a forest - that Tafi made his move. He first led the chase behind a group of early breakaways led by Steels, the winner of Ghent-Wevelgem last week, and, despite a puncture with just over 30 miles left, shook off his rivals one by one.
Andrei Tchmil, the Milan-San Remo winner who won the "Hell" in 1994, was among the first favourites to lose ground. Ballerini quickly followed. And, with 25 miles left, two of the most promising riders in the bunch, Belgium's Franck Vandenbroucke and the American champion George Hincapie, were still in contention in a small group led by Tafi.
Steels, Peeters, and two Paris-Roubaix specialists, the Dutchman Leo Van Bon and the Belgian Jo Planckaert, were also in the group. But when Tafi struck the final blow at another classic spot of the race, le Carrefour de l'Arbre, none of his rivals could reply.
Tafi, a former winner of the Tour of Lombardy, remained on his own for the last hour of the race and he was never threatened on the run to the finish.