After a tight first half had ended scoreless, the visitors took the lead when Oscar Cardozo finished off a flowing counterattacking move. Leverkusen gave everything in search of an equaliser but it proved to no avail as Benfica claimed the advantage heading into next Thursday's second leg.
Amid falling snow and on a greasy pitch, neither side managed to dominate possession for any great spell and chances were at a premium in the opening 45 minutes. Jonathan Urreta saw an early shot comfortably saved by Bernd Leno in the Bayer goal, before Gonzalo Castro half-volleyed Jens Hegeler’s cross wide of the post.
There was plenty of industry on show from Leverkusen in attack, with Castro and Andre Schürrle especially busy. They couldn’t muster much of a threat on goal, however, and Schürrle wasted their Bayer's opportunity with an under-hit cross to Kießling that was easily cleared.
Sidney Sam replaced Schürrle at the half-time break, but it was the away side that made the breakthrough just after the hour-mark, and they did so in stylish fashion, as a skilful move ended with Cardozo dummying a defender and clipping a delightful finish past Leno from eight yards.
Sami Hyypiä’s men responded well and after Michal Kadlec had contrived to miss from five yards, the impressive Hegeler forced two excellent saves from Benfica keeper Artur Moraes. The home side laid siege to Moraes’ goal in the final few minutes and almost forced a leveller with the last kick of the game, but Sam’s chip was dramatically cleared off the line by Lorenzo Malgarejo, as the Portuguese side held on.
Leverkusen: Leno – Hosogai (Boenisch, 82‘), Schwaab, Wollschied, Kadlec – Rolfes, Bender, Hegeler – Castro (Milik, 70‘), Schürrle (Sam, 46‘)- Kießling
Benfica: Moraes – Andre Almeida, Luisao, Garay, Malgarejo – Gomes, Matic, Gaitan – John, Urreta (Salvio, 58’) – Cardozo (Lima, 71’)
Goals: 0-1 Cardozo (61’)