The 27-year-old was one of the standout performers as Saints reached the Capital One Cup last 16 with a 2-0 win against Bristol City.
Merely turning out in the third-round tie marked quite a turnaround for Lee as just weeks ago his Saints career looked to be over.
Barely used last term, he was farmed out to FC Tokyo on loan for the latter part of the season and told he had no future at St Mary's upon his return.
However, manager Mauricio Pochettino had a change of heart after being impressed by Lee's attitude and aptitude, leading to his return to the side against the Robins.
"He played very well," assistant Perez said. "We were talking on the bench about his performance, especially in the first half.
"He was very dynamic, he played not only as a forward but also tried to help team link up and build between the lines.
"I am really, really happy with his performance. It is good news."
Lee was one of 11 changes made by Saints, with Adam Lallana and Jay Rodriguez the only two starters from Saturday's win at Liverpool included in the 18-man squad.
Gaston Ramirez and Jos Hooiveld netted as Pochettino's side secured safe progression, although a much improved second-half performance from City meant it was a far from easy win.
"We were obviously made to work hard in the second half," Perez said. "I thought the game was difficult.
"We scored in the first half but the opponent played well. They played without pressure.
"We are very happy about the result because it became a hard training session towards the end of the game.
"We know it is difficult to play as a team when you've made 11 changes, but this type of game, the cup games, we have to fix these kind of problems.
"We know it is not for the players playing the best football.
"I think Bristol played well and it was not easy for us to get the ball back and play with possession.
"At the end of the game, when Harrison Reed and Jay Rodriguez came in it helped the team create the level and tempo.
"It was because the opponent played well, not because we dropped off that they were better in the second half. They got some chances to score so it was difficult."
It was a performance that belied City's lowly position in the League One relegation zone, giving manager Sean O'Driscoll hope.
"I am pleased with the way the players performed, pleased with the way we approached the game," he said.
"We got stronger as the game went on, which is pleasing.
"We came to terms with their possession, which you expect when you play a top team."