Tsipras's Syriza party was on course to claim 35.3 percent of the vote.
Leaders vie to steer country through economic reforms, refugee crisis.
Spain's far-left party have declared their intent to follow in Syriza's footsteps after election triumph.
Syriza won 149 seats in the 300-seat parliament, two short of an absolute majority.
Syriza was on track to take 36 and 38 percent of the national vote.