 Lumsdon began his career at Sunderland, making his first-team debut against Wolverhampton Wanderers on 7 February 1998.In the same week, he signed a five-year professional contract, and was also called up to the England under-18 squad.He was part of the Sunderland squad that won the Championship title in the 1998–99 season under manager Peter Reid, although he didn't make an appearance in the League that season (his sole appearance coming in the League Cup on 27 October, where he came on as a late substitute for Martin Smith in a 2–1 victory over Grimsby Town).