Complex sentence: UEFA Cup Winners' Cup is also the only European competition to have seen a third Croatian club reach the last sixteen, when Varteks advanced to the quarterfinals in 1998--99, in the last edition of the competition.
Split into simpler sentences: UEFA Cup Winners' Cup is also the only European competition to have seen Croatian clubs other than Dinamo and Hajduk reach the advanced stages. Rijeka reached the quarterfinals in the 1979--80 edition, while Varteks advanced to the quarterfinals in 1998--99, the last edition of the competition.