Munich - Bayern Munich's stars have been reminded of their 2013 treble under "father-figure" coach Jupp Heynckes after scoring eight goals without reply in their two games following his return.
"He's brought the energy and passion which he had in 2013," enthused Bayern captain Thomas Muller, who scored in their 3-0 Champions League win against Celtic on Wednesday.
Heynckes is a Bayern legend.
In 2013 he steered the club to the treble of Champions League, German Cup and Bundesliga titles.
No other German club has achieved the feat before or since.
The 72-year-old came out of four years of retirement a fortnight ago to replace Carlo Ancelotti, who was sacked immediately after the 3-0 debacle at Paris Saint-Germain.
Heynckes is now the oldest coach to have plied his trade in the Champions League.
"Age is just a number -- he is fresh and is up for it," said Arjen Robben, who hit the winner four years ago in the 2-1 victory over Borussia Dortmund in the 2013 European final at Wembley.
German defender Jerome Boateng, who admitted he thought of quitting Bayern under Ancelotti, describes Heynckes as "a mixture of football coach and father figure".
As Celtic coach Brendan Rodgers put it, Bayern have enjoyed a "bounce effect" under Heynckes, thrashing Freiburg 5-0 last weekend before beating the Scottish side.
The win over Celtic got Bayern's Champions League campaign back on track, placing them firmly in second place in Group B, three points behind PSG.
And the victory at Freiburg put them two points behind Dortmund in the Bundesliga table.
Bayern director of sport Hasan Salihamidzic said a "jolt" went through the team when Heynckes returned for his fourth stint at the club.
"I have the impression that he was never really gone," said Bayern chairman Karl-Heinz Rummenigge.
"Jupp is the ideal coach now -- he is the fittest 72-year-old I have ever known."
Despite the feel-good factor, Heynckes remains focused on fixing the team's lingering problems.
Bayern surrendered two-goal leads in draws against Wolfsburg and Hertha Berlin on either side of the PSG disaster.
"We really need to improve a lot," said Heynckes.
"There are other teams in Europe who are certainly playing better than us."
Freiburg and Celtic were also easy tests -- more difficult challenges lie ahead.
Bayern face RB Leipzig twice next week, in the Bundesliga and German Cup, then current league leaders Dortmund away in a fortnight.
Their Champions League showdown with Group B leaders PSG comes in December.
Against Celtic, Heynckes pointed to Bayern's inability to finish chances -- 29 shots on goal yielded just three goals.
But Bayern fans have reason for optimism.
There is the return to form of Mueller, back in his preferred position of attacking midfielder, happily roaming behind hot-shot striker Robert Lewandowski.
Joshua Kimmich, who has scored three goals at right-back, is firing in silky crosses for the likes of Lewandowski.
Centre-backs Boateng and Mats Hummels are re-establishing their World Cup-winning partnership.
"These are the first steps," said Heynckes, troubled by Bayern's dip in the second half against Celtic.
"This must not happen to a team like ours, you have to be wide awake from the first to last minute."
Rummenigge said that is exactly why Heynckes has been brought in: "He always finds the hair in the soup."
Heynckes has restored Mueller and Boateng, who both struggled under Ancelotti, to the starting line-up, putting several stars on the bench.
Arturo Vidal, James Rodriguez and record-signing Corentin Tolisso will get their chances in the coming games, Heynckes has said.
As Robben puts it, Bayern will need their entire squad in harmony to win a sixth-straight German league title and put up a challenge the later stages of the Champions League.
"If you want to win titles, you need that chemistry and cohesion," said Robben.
Kimmich took it further: "We are so far along that we can win all our games.