The Ag2r La Mondiale rider is also 11th on the General Classification, 54 seconds behind new race leader Porte.
Philip Deignan (United Healthcare) was next best in 31st, a minute and a half down.
Ronan McLaughlin (An Post Sean Kelly team) was away with eight others in a break for much of the stage, only to be dropped by his breakaway companions with less than half the stage to race.
McLaughlin finished 20 minutes back with the other Irish rider in his team, Conor McConvey.
Today’s fourth stage takes the riders 186 kilometres from Vilamoura to Tavira.
Elsewhere, Andre Greipel took his second stage win at the Tour of Oman and now holds a six second lead at the top of the GC.