The 26-year-old Olympic champion, who claimed a third successive World Cup title last season, played second fiddle to Magnus Moan during the opening round in Lillehammer as the Norwegian won both scheduled competitions.
Second in the first event and fourth in the second, there was to be no denying Lamy-Chappuis as the World Cup moved to Finland as he led after the ski jumping and then powered to victory in the cross-country skiing phase.
The Frenchman recorded by far the best total in the ski jumping with his effort of 139.3 almost four points clear of Slovenia's Marjan Jelenko and giving him a 15-second cushion ahead of the ski.
And, despite the best efforts of Magnus Krog, who won in Kuusamo last year, Lamy-Chappuis' time of 26:49.5 was enough to give him victory by 13 seconds over the Norwegian.
Well down in 13th after the ski jumping and 57 seconds behind Lamy-Chappuis, Krog put in a remarkable ski to finish second while there was double celebration for France as Sebastien Lacroix ended third.
Lacroix's rise through the field was equally, if not more, impressive than Krog's as, over a minute behind Lamy-Chappuis following the ski jump, he finished just 13.2 seconds shy of his team-mate to deny Eric Frenzel third by half a second.