If West Ham arrived here in Germany under the acceptance that a one-goal defeat would be a decent result, then it figures that 2-0 might have felt around about par.
Certainly, it was no less than Xabi Alonso's dominant side deserved; they held almost three-quarters of possession, completed in excess of 450 more passes and managed 33 shots to West Ham's one.
True, the goals came late, one off the boot of Jonas Hofman seven minutes from time, then the killer from the head of Victor Boniface in the first of that added on. But scoring late is what Leverkusen do, almost as much as losing is what they do not.
This was a 42nd match unbeaten for the German champions-elect this season, and should they extend that to 43 when Werder Bremen come here on Sunday, they may well head to London next week with a first-ever Bundesliga title secured.
So why, then, did it feel so cruel for David Moyes and his side, who were theoretically within seven minutes of halfway house parity, but visibly always clinging on?
Perhaps it was for the feeling that, on the night at least, neither he nor they could have done a great deal more.
Hamstrung by the absences of Jarrod Bowen and Edson Alvarez, in particular, there were few who thought the shift to a back-five an unnecessary act of caution, captain Kurt Zouma for the most part outstanding in leading the stand from its core. Behind them, Lukasz Fabianski was even better, making a sequence of acrobatic stops that belie the fact he will turn 39 on the morning of next week's return.
Up front, Michail Antonio was a lonely man, but that is just how he likes it on nights like these, all chest and elbows in bullying Jonathan Tah to forge the visitors' only real opening of note. That Mohammed Kudus scuffed it tamely at Matej Kovar in the home goal was the evening's one glaring regret.
"We did a really good job defensively," Moyes said. "[But] we were aware of them scoring late goals and they put us under intense pressure and we found it difficult."
But if absolved of blame on the night, then a more scrutinous eye would see this as the day when the failings of January's transfer window bit hard. Then, Said Benrahma and Pablo Fornals were allowed to leave the club without a replacement being signed.
Neither was first-choice, nor anything like the form versions of themselves, but the pair had still made 45 appearances between them across the first half of the campaign, minutes and miles that have had to be redistributed onto already overburdened legs since.
So it was, that where Alonso had eventual goalscorers Boniface and Hofman to bring off his bench, Moyes had, well, not much at all.
You could not exactly hang your hat on the idea that Fornals' scurrying energy might have made a difference, as it did when he charged through for a late winner at AZ Alkmaar in last season's Conference League last-four. Still, it would have been nice to have that — or any other — option.
Should Bowen fail to recover from a back injury in time, January's negligence will be made even more plain. Chasing the tie, with Emerson and Lucas Paqueta suspended, Moyes may have to start one of Ben Johnson and castaway Maxwel Cornet on the wing.
Before then, the Scot faces another daunting task in trying to raise his shattered side for Sunday's visit of Fulham. Into the Premier League run-in, the race for Europe is well and truly on. The road to Dublin, though, may just have been closed.
