 On 31 August 2013, Ki joined Sunderland on a season-long loan with a mid-season re-call option.He scored his first goal for Sunderland on 17 December 2013 in a 2–1 League Cup quarter-final win over Chelsea, cutting inside Ashley Cole then beating goalkeeper Mark Schwarzer with a low shot in the 119th minute for the winning goal.On 26 December, he scored his second for Sunderland in a 1–0 away win over Everton.