Saints swept past Barnsley in Round Two, winning 5-1 at Barnsley to set up a home game against the Robins, who knocked out top-flight Crystal Palace last week.
City, who were relegated to Sky Bet League 1 at the end of last season, last visited St Mary's in December 2011, when they won 1-0 to end our hopes of going unbeaten at home through that calendar year.
Tickets for this match will initially go on sale to 2013/14 Season Ticket Holders at 9am on Thursday 5th September, before General Sale commences at 9am on Wednesday 11th September.
There will be 20 loyalty points available for this game, with tickets priced at £18 for adults, £14 for concessions (over-65s and 17-21s), £10 for under-17s and £5 for under-11s.
Match tickets can be purchased online via our ticketing site
, by calling the ticket sales hotline on 02381 780 780
or in person from the Ticket Office.