Amica didn't stay in the second division for long, because the following season they again won promotion, this time to the Ekstraklasa under Marian Kurowski who took over the job started by former coaches Bogusław Baniak and Horst Panic.

On 13 June 1998, Amica Wronki beat Aluminium Konin 5–3 to win their first Polish Cup and first trophy in their history.

Impartial observers, such the manager of Lech Poznań Adam Topolski, chairman of Olimpia Poznań (a top flight club at the time) Bolesław Krzyżostaniak, the chief of Zawisza Bydgoszcz Edward Potok and former Górnik Konin manager Janusz Białek were all highly critical of the match they have witnessed.

The director of Amica Wronki at the time, Ryszard Forbrich, known as "Fryzjer", was later revealed to be the leader of an organised crime group, fixing matches all around the country, instrumental to a huge corruption scandal in Polish football.

The 1998 cup final however was never investigated, with trophy still belonging to Amica, and remains a sore point for Górnik fans to this day.

After a disappointing 1998–99 league campaign where they finished in 12th place, they managed to end the season well by winning their second Polish Cup by beating GKS Bełchatów on 13 June 1999.

They were drawn against Spanish team Atlético Madrid in the second round of the Uefa Cup and lost 5–1 on aggregate, before ending the 1999–2000 season in sixth place.

A penalty shoot-out was needed for Amica to beat Hungarians Budapest Honvéd FC 5–4 after a 1–1 aggregate tie in the second qualifying round of the 2004–05 UEFA Cup.

A 2–1 victory in the first round against Latvians FK Ventspils was followed by their first appearance in the revamped UEFA Cup group stage.

They played their last game in the Ekstraklasa on 13 May 2006 with a 2–1 win over GKS Bełchatów and finished in 4th place in the final league standings.

[5] Allegedly, one of the main reasons that the merger was finalised was the Amica company wanting to invest in a team with a larger fanbase.

Another reason was that Lech Poznań were looking for a new sponsor to inject funds into the team and Amica fit the bill perfectly since they were so close.

They lost 4–1 on aggregate against Moldovan team FC Tiraspol in the UEFA Intertoto Cup and had to contend with a season without European football in Poznań.