Spurs were pegged back by Sofiane Boufal's strike in a 1-1 draw at St Mary's in the first meeting and looked set to be knocked out of the competition when they trailed 2-1 in the return game at Tottenham Hotspur Stadium.

Tanguy Ndombele's shot deflected in off Jack Stephens to give the hosts the lead against the run of play, but Shane Long profited from some poor Hugo Lloris goalkeeping to level before the break.

Danny Ings then put Southampton in front 18 minutes from time, only for Lucas Moura to fire in an equaliser and Son to convert from the spot after he was fouled by Angus Gunn, setting up a home tie with Norwich City in the next round.