A first-team regular from the start under manager Gordon Lee, Horton played 40 games in the 1970–71 season, and scored his first competitive goal in a 3–2 win against Bury at Gigg Lane. He then found his scoring form in the 1971–72 campaign, as he hit eight goals in 47 appearances; he also became the club's penalty taker, with half of his goals coming from the spot. He hit seven goals in 43 games in the 1972–73 season, four of his strikes coming from the penalty spot. He missed a period around Christmas due to injury, and during this time his teammates struggled to find results; this ultimately cost the "Valiants", as they finished four points behind promoted Notts County. The injury had come in a 2–0 defeat at Charlton Athletic, when a knee-high tackle left him with a hairline fracture of the leg, which also caused him to miss an FA Cup third round tie with West Ham United.