Born from Belfast, Northern Ireland, Blayney started his career with Premiership side Southampton and was loaned out to Stockport County, but was cut short by a broken finger. He also he had a spell at Bournemouth on loan. He made his début for Southampton in May 2004, receiving a high amount of praise. Blayney also won Sky Sports save of the season after saving an Alan Shearer header in May 2004 on his Premier League debut. The match at St Mary's ended in a 3–3 draw. Blayney also played in the following 2–1 defeat at Charlton. Blayney would play two more games for Southampton the following season, the 2–2 Premier League draw against West Bromwich Albion and the 5–2 League Cup loss against Watford. Blayney, who was then behind Antti Niemi and Paul Smith in the team's pecking order went on loan to Rushden & Diamonds and Brighton & Hove Albion. Brighton tried to sign Blayney on a permanent basis in 2005, but could not afford the transfer fee Southampton were asking. Blayney did return to Brighton & Hove Albion for a second loan spell, before returning to Southampton in mid-December.