Substitute Stuart Armstrong struck late to earn Southampton an FA Cup fourth-round replay with a draw at Championship rivals Watford.
Matheus Martins' early free-kick had looked like being enough for the home side until the Scotland international levelled in the 89th minute.
The Saints, who arrived at Vicarage Road unbeaten in 21 games, struggled to reach their usual heights after making a number of changes.
Watford had created the better chances but failed to put the game to bed.
The hosts struck inside five minutes after quick thinking from Martins. He whipped a free-kick low into the near post from the left-hand corner of the area, giving Joe Lumley no chance.