The Scotsman had seven birdies and an eagle in a seven-under-par 65, leaving him one shot in front of Jeremy Robinson, of Britain, and two ahead of Sweden's Robert Karlsson and the Italian, Manny Zerman.
Torrance, who this month has finished third in New Orleans, 33rd in the US Masters and fourth in last week's Catalan Open, said: 'Being out late meant the greens were not at their smoothest, but I played beautifully and holed some nice putts.'
Robinson was a member of the 1987 Walker Cup team, but since turning professional later that year has not managed a top four finish.
His 66, made early on when the course was at its most benign, contained a chip-in from 30 yards on the short fifth and five other birdies where superb approach shots left the 28-year-old needing to hole nothing longer than six feet.
Ian Woosnam has seven strokes to make up after his 72. The Welshman described his play as 'terrible', but found one encouraging sign.
'I tried using my shoulders more on the practice range before I went out and I started hooking the ball again,' he said. 'That's good and I'll stick with it for a while.'
CANNES OPEN Leading first-round scores (GB or Irl unless stated): 65 S Torrance. 66 J Robinson. 67 M Zerman (It), R Karlsson (Swe). 68 J Townsend (US), M A Martin (Sp), B Lane, P Fulke (Swe), A Coltart, S Grappasonni (It), P Mitchell. 69 T Price (Aus), R Drummond, G Orr, S Luna (Sp), S Richardson, D J Russell, T Johnstone (Zim), G Evans, D Clarke, W Riley (Aus), A Binaghi (It), M Wills.Reuse content