Porto will be without defensive midfielder Fernando for the second leg in Spain, after he was sent off for two late yellow-card offences.
Porto went into the game against Sevilla having won their last three matches at home including a 1-0 victory over Napoli in the last 16.
They took the lead after 31 minutes when Mangala headed home emphatically from Ricardo Quaresma's superb cross from the left.
Swiss side Basel took a huge step towards a second successive last-four appearance as Matias Delgado scored twice and Valentin Stocker netted a third in injury time in a 3-0 win over Valencia played behind closed doors.
The muted atmosphere did little to hamper the hosts who took the lead after 34 minutes, Delgado finding the net with a precise finish from the edge of the area.
That was the first goal Valencia had conceded in 400 minutes of Europa League action but their back line was breached for a second time four minutes later when the same player finished from close range.
Stocker gave Basel a comfortable lead to defend in the tie when he lifted the ball over Valencia keeper Vicente Guaita in stoppage time.
AZ Alkmaar were the only quarter-finalists who remained unbeaten from the group stage this season and would have taken the lead against last season's runners-up Benfica were it not for two good stops from Artur.
The visiting keeper saved with his legs to deny Aron Johannsson and then acrobatically kept out a swerving effort from Steven Berghuis in the first half.
However, the Dutch side fell behind three minutes after the restart when Salvio showed excellent technique to control a volley after some comically bad defending by the home team resulted in AZ keeper Esteban saving from Oscar Cardozo.
- Sports & Recreation
- Ricardo Quaresma
- Carlos Bacca
- Matias Delgado