Five goals by Goran Sablic had ensured that Watford led for most of the match. But they had a scare at the start of the final period when goals by Josh MacLean and Panagiotis Logothetis brought Southampton back from 7-5 down to 7-7.
That's how it stayed until 1.26 from the end when a goal by Ciaran Walshe secured a fourth win for Watford.
Photo (Trevor Hyde): Goran Sablic (blue cap) fires in another shot at Southampton goalkeeper Mike Sheath.