Lanterne Rouge who beat Merckx
Pierre Matignon, a French rider, won Stage 20 of the 1969 Tour de France (to the Puy-de-Dome) when he was the last-placed rider.
Matignon was competing with another Frenchman, Andre Wilhelm, for the Lanterne Rouge, but after Matignon fell so far behind overall, Wilhelm attacked on Stage 20. After he was caught, Matignon attacked and had a 7:30 lead with 20km to go. Eventually Eddy Merckx joined the chase, and only Raymond Poulidor and Paul Gutty could stay with him.
Matignon won by 1:25, too exhausted to give a victory salute. But Wilhelm ended as the Lanterne Rouge, and Merckx, of course, won the Tour.
This is from the book The Yellow Jersey companion to the Tour de France, edited by Les Woodland, a great book for Tour history. But you can also look at Matignon's wikipedia article for more.