The disclosure reversed the order of finish reported by the state electoral commission a few hours before, in which it said the ruling HDZ had beaten the allied Social Democrats (SDP) and Social Liberals (HSLS) by a razor- thin margin.
State electoral commission chairman Ivan Mrkonjic announced the SDP had finished with 24.18 per cent and HSLS with 12.58 per cent in Sunday's election for a combined 36.76 percent while the HDZ tallied 35.67. This did not necessarily mean the opposition would take over the powerful Zagreb regional government, as the HDZ was as the biggest single vote- getter and its rivals fell short of a viable majority.
With the result so close, any change of power looked fraught with problems in a country where effective one-party rule with a democratic veneer has prevailed for decades, by communists until 1990 and by nationalists since then.
The SDP and HSLS led a seven-party bloc to victory over the HDZ in Zagreb's 1995 municipal elections. But Mr Tudjman vetoed four opposition mayoral nominees on "national security" grounds.
The President's manoeuvre was condemned in the West. Mr Tudjman argued the HDZ had won a "relative majority" while the opposition was an unstable mishmash of parties ranging from far-left to far-right.
Former rebel Serbs took part in a Croatian election for the first time but voting in the enclave of Eastern Slavonia was delayed by technical glitches.
Serbs in Eastern Slavonia, which is to be reintegrated into Croatia this summer after a period under UN protection, got an extra day to vote on Monday to compensate for organisational bungling.