Nuremberg’s defeat also boosted Hamburg SV’s survival hopes and VfB Stuttgart pulled away from danger by beating third-placed Schalke 04 3-1, helped by a brace from Martin Harnik.
Leverkusen (54 points) leapt above VfL Wolfsburg (53) into fourth place which earns a place in the Champions League playoff while Schalke (58) are still on course to go straight into the group stage.
Nuremberg (26) stayed one off the bottom and Hamburg SV, the only ever-present team in the Bundesliga’s 51-year history, are one point and place above them in the relegation playoff spot. Stuttgart, 15th, opened a four-point gap on Hamburg.
Defender Spahic put Leverkusen ahead in the 16th minute when he met a loose ball and fired home from 30 metres.
Nuremberg were level within 10 minutes when Marvin Plattenhardt’s free kick, seemingly intended as a cross, evaded everyone and went straight into the net.
The hosts should have gone ahead early in the second half when Josip Drmic went clear on Bernd Leno who saved his effort and blocked the rebound from Hiroshi Kiyotake.
Almost immediately, Boenisch put Leverkusen back in front after Nuremberg defender Mike Frantz missed a chance to clear the ball.
Leverkusen’s third came after they cleared a Nuremberg corner and Son Heung-min ran from one penalty area to the other before laying the ball into the path of Spahic for a simple finish.
Son was also involved in the fourth as his shot was mishandled by goalkeeper Raphael Schaefer and, although it fell to Plattenhardt, the Leverkusen defender headed straight to Hilbert who gratefully converted the fourth.
The other game pitted Stuttgart coach Huub Stevens against the club at which he had two stints in charge.
Two goals from Austria forward Harnik and one from former Germany striker Cacau put Stuttgart three ahead in just under an hour before Adam Szalai reduced the arrears for Schalke.
(Reporting By Brian Homewood, editing by Ed Osmond)