Jose Mourinho admitted the game-changing substitution that helped inspire Tottenham's comeback win against Olympiakos was born out of necessity to help the team and not done to hurt Eric Dier.
Spurs trailed 2-0 to Youssef El Arabi and Ruben Semedo goals inside the opening 20 minutes as Mourinho's first home game in charge of Spurs threatened to turn into a nightmare.
But the Portuguese acted swiftly, replacing defensive midfielder Dier for attacking midfielder Christian Eriksen on 29 minutes, a move that swung the game in the North London club's favour.
Dele Alli reduced the arrears in first-half injury time before a second-half Harry Kane brace and a superb strike from Serge Aurier sent Spurs into the last 16 of the Champions League.
It was a second successive win for Mourinho since replacing Mauricio Pochettino last week following Saturday's 3-2 Premier League win over West Ham United.
Rather than milk the applause for the tactical change of replacing Dier with Eriksen, Mourinho said it had been the hardest part of his evening.
"The most difficult moment for me was not the goals but the change I had to make," the 56-year-old, whose tactical acumen has earned him silverware at every club he has managed, told reporters. "It hurt the player but also hurt me. It was not easy for the player or me.
"But it's important the player understood and I was fortunate that it was a very intelligent boy who understood it was about the team not the performance. I apologised to Eric and made it clear I didn't do it to hurt him.
"Christian gave us what we needed at that time."
Mourinho, sacked by Manchester United last season after his reign there turned sour, has been charm personified since swapping punditry for the Tottenham job.
As well as praising his players' response to adversity on Tuesday, and the fans, he also waxed lyrical about a ball boy, whose sharp thinking allowed Aurier to take a quick throw-in that ultimately led to Kane's 50th-minute equaliser.
"To do that you have to be a very good ball boy," Mourinho said with a straight face. "I was, between 10 and 16 years old a very good ball boy and he was a very good ball boy.
"He was reading the game and wasn't looking at the stands. I wanted to invite him to the dressing room to celebrate with the players but he had disappeared."
Spurs have now scored seven goals in winning Mourinho's first two games in charge to make a good first impression on many supporters unconvinced by the appointment of a former Chelsea manager renowned for a more conservative style of football.
Though Eriksen's introduction gave Spurs a more attacking thrust, they were offered a route back into the game owing to a huge error from Olympiakos.
Aurier's low cross from the right should have been easily cleared by Yassine Meriah, but he let the ball slip under his foot and Alli was on hand to tap in at the back post in first-half stoppage time.
Five minutes after the restart, Spurs were level as Aurier's throw-in freed Moura down the right and his cross was swept home by Kane.
Aurier was the unlikely hero 17 minutes from time as he sweetly connected with Alli's cross at the back post to put Spurs in front.
And Kane put the seal on morale-boosting second half when he stooped to head home his 23rd goal of the season in as many games for club and country.
"We know that and did not come out with any energy and they got the two goals and put us under pressure, it was an uphill struggle but we got the goals and it feels good to qualify," said the England captain.
"It was about qualifying, no matter how we did it."
Last season's Champions League finalists can now look forward to the knockout stages for a third straight season, but will go through in second behind Bayern Munich in Group B after the German giants secured top spot with a 6-0 thrashing of Red Star Belgrade.
Robert Lewandowski scored four goals in the space of 16 second-half minutes, the first of them a penalty, in between goals by Leon Goretzka and Corentin Tolisso.
Lewandowski has scored four times in a Champions League game once before, for Borussia Dortmund against Real Madrid in 2013. He now has 27 goals for Bayern this season.
"I am just as happy when I don't score and we win," the Polish striker told German Sky.
