Heung-Min Son came back to haunt his former club with his first-ever Bundesliga hat-trick helping Bayer Leverkusen to a 5-3 victory over Hamburg.
The South Korean, who switched clubs in the summer, helped the hosts race into a 2-0 lead, but Maximilian Beister and Pierre-Michel Lasogga brought Hamburg back on terms.
Son's third restored Leverkusen's lead before Stefan Kiessling gave them a cushion once again.
Lasogga brought Hamburg back into the game again before Gonzalo Castro sealed victory for Sami Hyypia's men, taking them back level on points with second-placed Borussia Dortmund.
The Son show started early on with the South Korean blazing through, beating Heiko Westermann before grabbing his first goal since the opening day of the season with a composed finish.
His second was even better as he once again used his pace to race away from Westermann and past Rene Adler before slotting the ball into the unguarded goal.
Hamburg responded with Beister drilling a low shot in from the edge of the penalty area, forcing Leverkusen onto the back foot.
The home team succumbed to a second when Lasogga struck early in the second half, but parity lasted just five minutes before Son rounded off his hat-trick in style with a placed volley into the right-hand side of the goal.
Son then turned provider to thread Kiessling through, and the German striker beat a forlorn Adler to confirm Hamburg's status as having the worst defence in the division.
Lasogga struck again with his eighth goal of the season giving the guests hope, but that was dashed as the visitors threw men forwards in search of an equaliser, Leverkusen breaking and Castro lobbing the onrushing Adler to complete the scoring.