Mousa Dembele was also back with Harry Winks missing out and Eriksen came in for the injured Harry Kane.
Janssen has struggled to play well for Tottenham this season and has not contributed much to the team.
Pochettino had insisted before the game his squad had the resources to cope with the loss of Kane, who was ruled out for up to six weeks after picking up an ankle injury in the FA cup quarter-final victory over Millwall seven days previously.
Neither player managed to get on the scoresheet, with Christian Eriksen and Dele Alli firing Spurs past the Saints, but Pochettino was pleased with the contributions they made.
On a day were Spurs really needed someone to step up and take the match by the scruff of the neck, they got just that as Eriksen showed his class from the start of the game. The Tottenham substitute, Vincent Janssen, who provided a focal point late on, nearly added a third for his team only for Forster to touch his fierce shot over the crossbar.
Meanwhile, Southampton hadn't played for 15 days - since winning 4-3 at Watford - and were eyeing revenge against Spurs, who had triumphed 4-1 in the previous meeting on December 28.
Pochettino's team hadn't been at their best, yet it had been enough to dominate an off-the-pace Southampton side. "But - now Harry Kane is out it's a big blow".
Claude Puel:"It will be interesting to see our progress".
There are no new injury worries for the Saints with Virgil van Dijk remaining a long-term injury absentee while Charlie Austin is close to returning from a shoulder injury.
Tottenham: Lloris, Trippier, Dier, Alderweireld, Vertonghen, Davies, Wanyama, Dembele, Eriksen, Alli, Son.
Southampton had their moments when the scoreline stood at 1-0 and there were winces on 28 minutes, in particular, when Dusan Tadic blazed over from the edge of the six-yard box, after Nathan Redmond had volleyed back Cedric Soares's deep cross.
On Harry Kane: "He is very positive, joking about (coming back) after the global break, three to four weeks".
"He's very positive and that is good, but at the same time we need to be careful with his injury. The victory keeps us in a very good position", Pochettino added. But the good thing he is very positive. "We are finding our best form now and the team is more solid".