McNab left Arsenal in the summer of 1975, and Nelson finally became Arsenal's first-choice left back. An aggressive, hard-tackling player, he was a crowd favourite and known for his cheeky sense of humour. For the next five seasons he was a near ever-present in the Arsenal side, and he played in all three of their successive FA Cup finals, in the starting eleven in 1978 and 1979 and as a substitute in 1980. The only win was in 1979, in which Arsenal beat Manchester United by a 3–2 scoreline. Nelson also played in the 1980 European Cup Winners' Cup Final, which Arsenal lost to Valencia on penalties.