The 34-year-old’s performances at Sunderland have belied his advancing years and led to a surprising international turnaround, having won the last of his 55 international appearances in November 2013.
He won his long-awaited 56th cap at Wembley, being deployed from the start as England looked to prise open the visitors’ well-drilled, packed defence.
The decision paid dividends as Defoe swept home Raheem Sterling’s cross midway through the first half to set England on course for a straightforward win.
“It’s a great moment for him,” Southgate said of England’s man of the match after his 20th international goal.
“He was thrilled to be back involved in the squad, I think he has enjoyed his week immensely.
“He’s been a good senior professional to have around the team, both in terms of the way he’s trained, his professionalism, which has been great for some of the younger players to see, and his finishing in training and then today, which we expected really.
“I would have put my house on him scoring at some stage today, so I think he’s had a really positive impact on everybody.”
Defoe, who has established himself in Southgate’s thinking in the absence of Wayne Rooney, Harry Kane, and Daniel Sturridge, struggled to keep his emotions in check as he wound back the years at Wembley, where he led the team out with Bradley Lowery, the terminally-ill five-year-old who calls the Sunderland striker his “best mate”.
Defoe, so devastated to be overlooked for the World Cup in Brazil three years ago, could even head to Russia next summer at the age of 35.
“I think we’ve got to look every time we get together as to who is in form,” Southgate said when asked if the striker was a realistic proposition for the 2018 World Cup.
“I don’t know if we can have a distinct pecking order because players that are playing well deserve the opportunity. If we are going to be successful, we have got to have that competition for places.
“The reality is we will always lose players to injury, we’ve never been able to field or pick a full cohort, so it’s really important that we are able to call upon the likes of Jermain and for him to have the impact he had in a game like today.
“But if he is scoring goals in the Premier League and playing as well as he has this season, then there’s absolutely no reason why he couldn’t.”
Defoe was withdrawn with 30 minutes left as England looked to put the game to bed against spirited Lithuania.
His replacement Jamie Vardy did just that six minutes after his introduction, completing a comfortable World Cup qualifying win that keeps England in control of Group F.
“I thought it was one of those afternoons where it’s job done,” said Southgate.
“I am not going to eulogise over the performance, but the overall week I think has been really positive in setting the tone of how we want to work. The players have got a good feel about them, a spirit and they see the direction we want to head. For sure, we’ll play better than we did today.”
“It’s hard to put into words really,” said Defoe.
“I had to keep my emotions (under control), obviously little Brad was with me. You can imagine how I felt doing that, it was special. Just to be back playing with the lads was a great feeling.”
Lithuania boss Edgaras Jankauskas was “amazed by the quality” of England’s players and proud of his side’s display at Wembley, where they held their own for large parts and frustrated Southgate’s side.
“I am very proud of my team because we have been tested by a tremendously strong team — probably the strongest team we have faced until now,” said the former striker, who won the Champions League at Porto under Jose Mourinho.
“We will take a lot of positives from this loss, to see what targets can be set because what we witnessed today in the first half was unbelievable how skilful all those attacking players are and what amount of pressure we were put under.
“So I am very proud of my team because they worked extremely hard. We for sure crossed their limits. I cannot say any bad word about them.”
Hart, Walker, Stones, Keane, Bertrand, Dier, Oxlade-Chamberlain, Lallana, Alli, Sterling (Rashford 60), Defoe (Vardy 60).
Setkus, Vaitkunas, Kjanskas, Klimavicius, Slavickas, Kuklys, Zulpa, Cernych, Slivka (Paulinius 87), Novikovas (Grigaravicius 54), Valskis (Matulevicius 74).
Ruddy Buquet (France)