Clark, who continues to take an anti-inflammatory drug, has played only four tournaments on the European Tour this year. But he has two second places and a ninth to his credit; if he wins this week he will climb from seventh to top position in the money-list.
Gordon Brand and Jim Payne also shot 69, but Brand felt he was unlucky not to be one shot less. He was four under par coming to the short ninth hole, his last, and needed a birdie two to tie for the lead.
Instead, his ball struck a branch overhanging the green and bounced into the trees, from where he took three more to get down.
Sam Torrance, the defending champion, shot a 70 and was 'well satisfied' after suffering back trouble earlier in the week.
HEINEKEN OPEN CATALONIA (Pals Golf Club) First-round scores (GB and Irl unless stated): 67 G Levenson (SA), T Levet (Fra), J-L Guepy (Fr). 68 W Riley (Aus). 69 J Payne, O Nordberg (Swe), G J Brand, H Clark. 70 O Karlsson (Swe), A Hunter, R Chapman, J Lomas, S Torrance, A Bossert (Swit), P Fowler (Aus), A Sorensen (Den), C Cassells, M-A Jimenez (Sp), M Mouland, J Coceres (Arg), G Brand Jnr, C O'Connor Jnr. 71 M Wills, F Lindgren (Swe), G Hjertstedt (Swe), M Davis, P Fulke (Swe), D Cooper, P Mitchell, D Hospital (Sp), P-U Johansson (Swe), S Ames (Trin), D W Basson (SA), S Bottomley, R Berhorst (Ger), J McHenry, J-M Canizares (Sp), F Nobilo (NZ), S Bowman (US), D Smyth.