Nathan Redmond found the net on his Southampton debut as Saints battled back from a goal down to take a point in Claude Puel's first competitive match as manager.
Puel opted to employ the diamond formation, with Oriol Romeu at the base and James Ward-Prowse partnering Steven Davis in the centre. DuÜan Tadić played in an advanced role, tucked in behind Redmond and Shane Long.
Meanwhile, Maya Yoshida and Matt Targett started in the backline alongside CÚdric and Virgil Van Dijk, with JosÚ Fonte and Ryan Bertrand missing out due to fitness issues.
Saints went close to breaking the deadlock within the opening minute, but Tadić saw his free-kick parried by Heurelho Gomes and the Watford defence eventually scrambled the ball away.
The first goal of the season at St. Mary's came for the visitors, with Etienne Capoue lashing past Fraser Forster after a knock-down from Troy Deeney teed up the Frenchman.
Tadić danced his way past a sea of yellow shirts before lifting a ball towards the far post, but Long could only nod wide.
Redmond volleyed wide before going closer yet moments later when his curling effort was turned away by Gomes.
The debutant would soon have his first goal in Saints colours, volleying in on his left foot after Gomes failed to deal with Davis' corner.
Yoshida flicked a delivery from Davis just over the crossbar, before Ben Watson, who had only come on as a substitute 10 minutes earlier, was given his marching orders for a foul on Long as he raced in on goal.
Redmond could have been forgiven for thinking he had won the game with five minutes left to play, but the offside flag denied him a winner after he fired past Gomes.
Saints were forced to settle for a point, as the Puel era began with a home draw.
Next up for Southampton is a trip to Manchester United on Friday the 19th of August - kick-off at 20:00.
SAINTS: Forster; CÚdric (Pied - 79'), Yoshida, Van Dijk, Targett; Romeu; Ward-Prowse (H°jbjerg - 54'), Davis; Tadić; Long (Austin - 83'), Redmond.
Unused Subs: McCarthy, Fonte, Clasie, Rodriguez.