Saints could make FA Cup history by becoming the first team to win the trophy on a penalty shoot-out.
The FA have confirmed that the May 17 final showdown with Arsenal will be settled on the day.
No side has ever won the world's greatest club knock-out competition on penalties before.
But it the scores are level at full time and after an additional 15 minutes each way of extra-time, a shoot-out will decide the winners.
The nearest the FA Cup final has come to being decided on penalties in recent years was in 1993 when Andy Linighan scored a last-minute extra-time winner for Arsenal against Sheffield Wednesday.
The FA also said that if Arsenal were to win both the FA Cup and the league this season, their opponents in next season's Community Shield would be the runners-up in the Premiership rather than the Cup.
Former Wessex League referee Keith Stroud has been named as one of the assistant referees for the FA Cup final.
Stroud, from Gillingham in north Dorset, was voted the best referee in the Wessex in 1999.
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