Manchester United ended a seven-game losing streak on the road in the premier league with a narrow win at Saints.
In the face of a spirited challenge, United were able to build on Monday night's thrilling victory over the Reds.
Bruno Fernandes scored the only goal of the game after the break to give United the three points they deserved.
The Saints, who will take heart from their performance, survived an almighty goalmouth scramble in the first half and were able to keep a clean sheet.
As they closed out their second successive win and first league triumph on the road since February, Ten Hag was able to introduce Casemiro as a late substitute.
If United slipped up at Saints, they would be accused of raising their game against their rivals.
Ten Hag will take great satisfaction from a clean sheet and three points, even though this was not a vintage performance.
There was a tight and competitive game in which United had to survive late pressure from the hosts with keeper David de Gea making a fine save from Joe Aribo's headed goal.
The visiting fans demonstrated their delight at the final whistle - while once more chanting their desire for the removal of owners the Glazers - and were also able to get a glimpse of new marquee signing Casemiro when he appeared as a late substitute.
This isn't a classic, but United and Ten Hag will take this as they embark on the slow rebuild from the crisis that threatened to destroy the club after defeat at home to Brighton and a humiliating loss at Brentford.
There's more to come.