Stage three of the Dauphiné Libéré was another roller coaster ride, featuring four major climbs, including the category two, 1,119-metre-high Col de Mezilhac coming with 36 km to go.
Portal broke away early from the pack to cross the line 51 seconds ahead of Tombak and Flores. Australian Stuart O'Grady finished fourth, leading the main peloton, which included five times Tour de France champion Lance Armstrong, across the line 1:49 adrift.
Also in the main peloton was Spaniard José Gutierrez (Phonak), who retained the overall race lead.
The stage was marred by a dangerous crash involving Mickael Pichon (La Boulangère), who fell into a ravine at km 153 while descending the Col de Mezilhac.
The badly injured Frenchman was immediately transported to hospital by helicopter with multiple fractures in his legs, collarbone and ribs.