The man challenging Tayyip Erdogan in Turkey’s presidential elections this weekend received a boost on Thursday when a small party candidate abruptly withdrew and a closely-watched poll gave him a more than five percentage point advantage.

The withdrawal by Muharrem Ince, one of four contesting Sunday’s presidential vote, could reshape the last days of campaigning in what is seen as Erdogan’s biggest test in his two-decade reign.

Turkey’s main stock index jumped 6% after Ince made the shock announcement in front of his party’s headquarters in Ankara. Financial markets are on edge given Kemal Kilicdaroglu has pledged to reverse Erdogan’s unorthodox economic policies.