The striker found the net as Werder eased to victory, and afterwards delivered a wry assessment of how he and fellow forward Eren Dinkci had ended up back at the club.
"Werder does it smartly, sells the players for a lot of money and gets them back cheap," Füllkrug said with a laugh.
Both players left Bremen for significant transfer fees before returning on cut-price loan deals ahead of this season, with the pair originally sold for a combined total of around €22m earlier in their careers.
Füllkrug's path back to the Weserstadion has taken in spells at Borussia Dortmund and West Ham United since he departed Bremen, along with a loan at AC Milan last season, before he returned on loan from West Ham this summer having accepted a pay cut to facilitate the move. Dinkci, meanwhile, arrived on loan from Freiburg just days before Füllkrug's own return was confirmed.
Füllkrug began his professional career at Werder before earning a big-money move to Dortmund, where prolific form for the Bundesliga club had first established him as a regular in Germany's national team.
His return to Werder Bremen represents his third spell in green and white, following an earlier stint between 2019 and 2023 that included winning the Bundesliga's top scorer award and helping the club secure promotion back to the top flight.
The victory over RB Leipzig offers an early sign that Werder's revamped attack, built around a mixture of loan reunions and cut-price returns, can deliver results this season. Head coach Daniel Thioune has spoken previously of Füllkrug's importance as a leader both on and off the pitch, and with seven new faces added to the squad over the summer, the club will hope this win proves the platform for a more competitive campaign than in recent years.
Füllkrug's second Bremen spell had been the finest of his career, culminating in a Germany call-up and a share of the Bundesliga golden boot in 2022/23 alongside former Leipzig striker Christopher Nkunku, who himself returned to the German top flight this summer on loan from AC Milan.
His subsequent moves abroad, first to West Ham and then on loan to Milan, produced considerably less impact, with injuries repeatedly disrupting his rhythm in England. A third stint at Werder now offers the 33-year-old the chance to rediscover the form that once made him one of the most feared strikers in the Bundesliga.