Borussia Dortmund coach Thomas Tuchel will welcome some close friends to the SIGNAL IDUNA PARK this Sunday when his former club 1. FSV Mainz 05 check in on him after five spectacular years spent together.

Read: Dortmund vs Mainz preview

Tuchel filled some rather capacious boots when he accepted Mainz's sporting director Christian Heidel's (Read: the man who made Tuchel and Klopp) invitation for his first major coaching role at Mainz in 2009, a year after Jürgen Klopp had left a superlative legacy. He succeeded in leading the club onto the next level – with two UEFA Europa League qualifications – before clearing his desk in 2014 for a studious sabbatical he deemed necessary, both for him and the club.

Lasting legacy

"It felt a bit like a teacher who, after five years, felt that it would instead be better for somebody else to explain things before such a tight bond started to stand in the way of progress," Tuchel explained to Die Zeit of his decision to leave Mainz over 18 months ago. That progress has since continued with Martin Schmidt (Read: Meet Martin Schmidt - the petrolhead coach) slipping suavely into Tuchel's size tens, and success again seems to be just around the corner for an unfancied club from Rhineland-Palatinate.

This weekend, Tuchel will be glad to see how his former club is continuing to flourish, as the master welcoming his pupil. "It's new for me because I used to be the one responsible for analysing the opponents," said Schmidt, who was Tuchel's right-hand man and joint tactical guru at Mainz. "I'm looking forward to this."

His challenge will be to outwit a man who was responsible for implanting a philosophy which continues to define the way Mainz play, even to this day. "There is certainly a signature that I am renowned for, and which we showed in Mainz, and that was a quick, attacking brand of football," Tuchel explained. "I stand for certain attributes: for an active style of play and for courageous defending, then getting the ball up front quickly."

'Defined aims'

Tuchel achieved the above on comparably limited resources to what he now has at his disposal in Dortmund, although Tuchel knows that merely having the likes of Pierre-Emerick Aubameyang, Marco Reus and Ilkay Gündogan does not, in itself, give you a big enough edge. "For me, a team is more than just the sum of all its players," he said.

"We had defined aims which enabled us to believe we could beat Dortmund, beat Schalke and even beat Bayern München, even when many thought it was not possible. Of course it didn't always work, but we were our own benchmark and the team often exceeded itself."

Under Schmidt, Mainz again are going above and beyond any statistics or expert opinion which may mark them down as intruders among the top five. The 05ers are where they are through tactical astuteness, discipline and determination. In short, they are where they deserve to be, and qualification for the UEFA Champions League next season is anything but Utopia.

Just a point separates Mainz from the play-off to the Champions League group stage, an additional point would take them straight in among Europe's elite. There is no pressure or obligation for them to succeed, though. "We just go to Dortmund as normal, without the thought that we have to do something spectacular," Schmidt said. "We just want to confirm our results from recent weeks."

'Continuing to push boundaries'

If they do that, Tuchel and Schmidt could be playing tactical chess again next season, and not only in the Bundesliga. Dortmund's qualification for the Champions League can be all but rubber-stamped with a win over Mainz, while the title would not be out of the question with a further three points either.

"We're just continuing to push our boundaries," said Tuchel after his side's 0-0 draw with FC Bayern München in Der Klassiker.

If Mainz can join them in Europe's elite club competition, it would be the continuation if not culmination of Tuchel's groundwork, furthered by Schmidt – the first to extend his hand to his friend and counterpart at the SIGNAL IDUNA PARK this Sunday.