Complex sentence: Victory in the 1984 Portuguese Cup final ensured Porto's return to the Cup Winners' Cup in 1984--85, but they were knocked out in the first round by Welsh Cup runners-up Wrexham.
Split into simpler sentences: Victory in the 1984 Portuguese Cup final ensured Porto's return to the Cup Winners' Cup in the 1984--85 season. However, they were knocked out in the first round by Welsh Cup runners-up Wrexham.