Jalabert, who has virtually secured his first major tour win with inspired riding throughout, completed the 179-kilometre 17th stage between Naut Aran and Luz-Ardiden in 5hr 34min 45sec.
He broke from the leading group a kilometre from home but Abraham Olano, his main rival for the title, put up a brave fight. The Spaniard finished in second place, five seconds behind, with Jalabert's ONCE team-mate, Johan Bruyneel, third.
The French mountain specialist, Richard Virenque, finished fourth in a stage which passed over two special category climbs, one of them the daunting Col de Tourmalet.
The Frenchmen, on home soil for much of the race as it crossed and re- crossed the border, took advantage of the absence of the Italian climbing specialist, Marco Pantani, who dropped out of the tour with fever before the stage started.
Jalabert, protected by his team-mates Bruyneel and Melcior Mauri, sat tight in a group of nine riders who broke early from the peloton and then attacked the mountains.
With eight kilometres remaining the group was whittled down to five and, with the line in sight on the road above, Jalabert broke and eased through the final three hairpin bends to claim victory, increasing his overall lead over Olano to more than six and a half minutes.