Celta Vigo moved a step closer to a maiden European semi-final by beating Genk 3-2 but the Belgians' away goals leave the Europa League quarter-final tie finely poised.
The sole Spanish representatives in the last eight had to come from behind after Jean-Paul Boetius gave Genk a dream start when he headed them into a 10th-minute lead.
The in-form Belgians found themselves behind just seven minutes later, after Pione Sisto and Iago Aspas took full advantage of Celta's first shooting opportunities, and John Guidetti made it 3-1 before half-time.
Genk were facing a mountain to climb in the second leg until substitute Thomas Buffel narrowed the deficit and they will take two precious away goals into the second leg at Cristal Arena, where they are unbeaten in European competition this season.
However, Celta have won their last three Europa League away games and if the likes of Guidetti and Aspas are firing they will be hard to stop, but Genk will hope that home advantage in the second leg proves decisive.
Genk themselves have been prolific scorers on their travels in Europe this season and it took just 10 minutes for them to open the scoring.
Leandro Trossard skilfully turned Andreu Fontas before his cross found the head of Boetius, whose close-range effort bounced off the body of Sergio Alvarez on its way into the net.
The visitors' lead was cancelled out four minutes later when Jonny's through-ball found Guidetti and the Swede's instinctive back-heel flick put Sisto through to side-foot the ball past Mat Ryan.
The turnaround was complete three minutes later when Aspas pounced on Omar Colley's poor clearance and struck a sweet, low drive that arced inside the far post, sending the home supporters into raptures.
Timothy Castagne fired over the crossbar from close range as Genk tried to regain the momentum they briefly enjoyed in the opening stages, but they were dealt a hammer blow seven minutes before half-time.
Celta broke with Guidetti, who exchanged passes with Aspas and then netted his fourth Europa League goal of the campaign from just inside the penalty area to give the hosts a two-goal cushion at the break.
Ryan saved well from Hugo Mallo early in the second half, but the introduction of Buffel after 62 minutes proved to be an important moment in the tie.
The 36-year-old had been on the field just five minutes when Trossard's cross was left to run by Jonny and though Alvarez saved Buffel's first shot, the goalkeeper was beaten with a header on the rebound.
Pablo Hernandez struck a thunderbolt that Ryan could only parry over the crossbar and Aspas forced the Australian goalkeeper to make a superb fingertip save as Celta pressed for a fourth goal that would have made the second leg much more comfortable.
That goal failed to transpire and Genk coach Albert Stuivenberg will fancy his side's chances in the second leg.