Liverpool boss Klopp would have been quite pleased with a 0-0 outcome at the Estadio El Madrigal in Villarreal as both defences kept a tight leash on the respective strike-forces.
But in the second minute of added time, Denis Suarez controlled a long ball out of defence and beat Kolo Touré on the right-hand side, and he squared it for Lopez to give manager Marcelino’s team a much-needed advantage ahead of the second leg next Thursday at Anfield.
While Liverpool have made great strides forward under German Klopp, he gave an indication of the type of result he was looking for by leaving England striker Daniel Sturridge on the bench as he rather deployed Welshman Joe Allen as a “false nine” upfront.
Allen had the occasional support runner in Roberto Firmino and Philippe Coutinho, but the packed midfield ensured that there were few openings for Villarreal’s strikers, former Tottenham man Roberto Soldado and the powerful figure of Cedric Bakambu.
The best Liverpool chance of the match came in the fifth minute already when the ball ricocheted into Allen’s path just inside the Villarreal box, but he delivered a feeble attempt on goal that went straight to goalkeeper Sergio Asensio.
While there was a lot of action between both penalty areas, the finishing left a lot to be desired as the defenders blocked most of the shots, although Bakambu’s header from a Villarreal corner hit the post.
Soldado also had opportunities on goal at the start and end of the first half, but one shot went across the goal and the other just didn’t curl in enough.
In a match that seldom raised the roof in terms of action, Firmino nearly broke the deadlock when he fired in a shot from inside the box, which Asensio got a hand to and deflected the ball on to the left upright.
Bukambu suddenly burst into life with three minutes left when he was put through on goal, but his left-footed attempt was well saved by Simon Mignolet.
In the same move, Liverpool counter-attacked through Alberto Moreno, who surged downfield but ran out of steam and blasted his shot over the top.
But just when it looked as if the Merseysiders had enough to escape Spain unscathed, they were undone by Suarez and Lopez.
In the other first leg semi-final in the Ukraine, Shakhtar Donetsk held a one-goal advantage for over 45 minutes before Kevin Gameiro scored the equaliser for Sevilla with a penalty in a 2-2 draw.
Victor Machin Perez gave the Spaniards the lead in the sixth minute, but the home side hit back with a double strike within 12 minutes from Marlos Romero Bonfim and Taras Stepanenko.
The Ukrainians thought they had done enough to claim victory, but Facundo Ferreyra fouled Perez in the box in the 81st minute, and Gameiro stepped up to level the scores.
Original source: Liverpool felled by late sucker punch