In a reversal of usual League Cup practice, it was the Premier League club who chose to field something approaching their strongest side here, while the Championship team made nine changes amid what their manager, Ian Holloway, called the “extreme physical test” of seven games in 22 days.
Not surprisingly in the circumstances, rank was pulled, although it took Southampton an awfully long time to make it count in a tie that finally provided some entertainment in the second half for a crowd of only just over 6,000.
Southampton have suffered several defeats by lower division sides in recent years. Whether aware of that or not, their new manager, Ronald Koeman, stuck with eight of the side who had drawn with West Bromwich Albion on Saturday, even if strong words may have been necessary at half-time to produce the desired result.
Far from being overawed, Millwall’s youngsters made by far the best opportunity of a dull first half. A long punt from their goalkeeper David Forde bypassed the whole Southampton team to leave Magaye Gueye clear, but the former Everton man miscued hopelessly wide.
Other than that it was poor fare, which Koeman tried to improve on with the introduction at half-time of midfielder Jack Cork for the more defensive Victor Wanayama.
The substitution worked better than he could have hoped when Cork rose to head the visitors in front from Dusan Tadic’s corner only six minutes after coming on.
There was more excitement in that period than during the whole of the first half, as Southampton finally disturbed the home defence. Forde had to save twice, from Tadic and the powerful Graziano Pelle, the latter then clipping a post from Nathaniel Clyne’s cross. They were still unable to relax until Pelle scored in added time.
Millwall (4-4-2): Forde; Hoyte, Williams, Webster, Briggs; Powell, Abdou (Thompson, 76), Chaplow (O’Brien, 63), Easter; Marquis, Gueye (Onyedinma, 63). Substitutes not used Godfrey, Gerra, Goodman, Siafa.
Southampton (4-4-2): Forster; Clyne, Yoshida, Fonte, Targett; S Davis, Wanyama (Cork, 46), Ward-Prowse, Isgrove (Tadic, 28); Pelle, Long. Substitutes not used Davis, Gardos, Ramirez, Taider, Stephens.
Referee D Whitestone (Northamptonshire).