"The Diamonds" continued to impress in the league, finishing first in Division Three and winning promotion the next season. Mills established himself as one of the club's first choice midfielders, playing in 30 league games. Likewise, in the next campaign, Mills played a further 30 games, though the club had far less success as they were immediately relegated back to Division Three. He did, however, score his first goal for the club that season in a 2–1 victory over Tranmere Rovers.