The Dutch side controlled large periods of the game without threatening the home goal too often, but take the advantage in the two-legged tie.
Having just about edged a tight opening 20 minutes, Slovan conceded the game's first real chance when Celso Ortiz found space just outside the box. However, his effort was straight at the goalkeeper.
Slovan came out firing after the break, forcing Esteban Alvarado into action from set pieces but AZ eventually took control again.
The pressure eventually told just a minute from time, when a long free kick fell to the feet of Viergever who fired beyond the goalkeeper..