Lucien Van Impe was second in the general classification with 2 ' 41" behind Raymond Delisle before the 14th stage of Tour de France 1976. The program of the day on the 10th of July 1976 was a 139 km long route in the Pyrenees between Saint-Gaudens and Saint-Larry-Soulan, including Col de Menté, Col du Portillon and Col de Peyresourde. The stage ended on Pla d'Adet, what was visited by Tour de France for the first time in 1974. (The race returned also in the subsequent year.)
Peugeot, Delisle's team clearly didn't intend to defend the yellow jersey on that day, thus the race was open. There was a very strong breakaway group, including Luis Ocaña, who despite his famous crash on Col de Menté in 1971, was almost unbeatable on this terrain. But he was not even in the top10 of the general classification before the stage.
Neverteless, Cyrille Guimard, the director sportife of Gitane-Campagnolo team wanted to have his rider Lucien Van Impe in the breakaway group. Van Impe was quite reluctant, but joined the riders at the front of the race. Meanwhile several riders closer to him in the general classification were struggling on the climbs.
Except Joop Zoetemelk, only six seconds behid Van Impe in GC, who simple miscalculated himself and thought that the breakaway won't survive. As he realised his mistake, he started to chase Van Impe and co, but it was too late.
On the last climb Van Impe rode away from his breakaway companions, and not only he won the stage but also took the yellow jersey. 8 days later he won also the general classification of Tour de France.
Lucien Van Impe is the only cyclist who was able to win a Tour de France stage up to Pla d'Adet twice. The second occasion happened in the 5th stage in 1981. It wasn't such a career defining moment for him as it was for the first time, but the mountain points he got for being the first on the top of the ascent certainly helped him to win the KOM yersey for the 5th time.