A little over three years ago, Thomas Tuchel decided that he would go out at the top. Literally. The then 39-year-old had just hiked 3,200 feet up a Swiss mountain with his Mainz 05 team to look at the sunrise as part of his pre-season preparation when it dawned on him that he couldn’t take his men any higher.

Tuchel had been promoted from youth to head coach two days before the start of the 2009-10 season without any prior experience at Bundesliga level. The former defender’s active career had seen him play only eight Bundesliga 2 games for Stuttgarter Kickers before a spell in the third division at Ulm under the maverick manager Ralf Rangnick – who opened his eyes to the novel concept of zonal marking and later encouraged him to start coaching – had been cruelly cut short by a debilitating knee injury in 1998. “I envied my Ulm team-mates for getting promoted soon after, I couldn’t take it,” he recalled.

That disappointment soon turned out to be the making of him, however. At newly-promoted Mainz, minnows with an annual budget of €15m, Tuchel succeeded by ignoring all football adages. You can only win with a settled team, versed in a specific system, they said. But Tuchel, an economics graduate – “I studied it to make my mum sleep better” – shuffled his side constantly, according to every game’s needs, and believed that Mainz could only survive in the league if they could play in a variety of styles, nigh impossible to predict for opponents.

“We didn’t want to break rules for the sake of it,” he said in a talk for a German thinktank. “We had to come up with ideas because we knew were inferior as a team.” Doing things differently included cutting corners: Tuchel forced his team to make diagonal runs towards goal, not play down the line, by changing the training pitch to a diamond shape. “If I tell them what I don’t want them to do, I’m a critic,” he said. “But my role is that of a service provider: I’m here to help and support the player.”

By the time he took a year off from football – just like his role model Pep Guardiola had done – a few months after his epiphany on the Swiss mountain, Tuchel had sensationally improved on Mainz’s seven largely successful years under Jürgen Klopp (2001-2008) by amassing more points than any team apart from the big hitters Bayern, Dortmund, Leverkusen and Schalke in five seasons, by taking them to the Europa League twice and setting a new Bundesliga record of seven successive league wins at the start of the 2010-11 season. “I couldn’t see how we could reinvent ourselves once more the coming summer,” he said of his decision to quit Mainz in April 2014.

Shinji Kagawa, Pierre-Emerick Aubameyang and Adrian Ramos celebrate during Saturday’s win over Werder Bremen. ‘It’s a gift to coach this team,’ says Thomas Tuchel. Photograph: Patrik Stollarz/AFP/Getty Images

During his sabbatical, he looked at other team sports, visited the Brentford owner Matthew Benham to understand the role of mathematics and stats in football and versed himself further in the teachings of Professor Wolfgang Schöllhorn. The sport scientist’s theory of “differential learning” contends that players do not learn by repetition and perfecting drills but by adapting their technique, intuitively, to a never-ending stream of problems. At the turn of the century, Schöllhorn’s ideas were adopted by the Barcelona youth coach Paco Seirullo, who later became Guardiola’s mentor.

Tuchel, who puts out every cone himself, has his players practising on slippery, extremely narrow or extremely wide pitches, makes them control the ball with their knees before passes and instructs defenders to hold on to tennis balls to stop them pulling the shirts of opponents. The aim is to make training so complex and mentally demanding that the game feels relaxing by contrast. “At first, we wondered what these things had to do with football but we realised quickly that they worked,” said Neven Subotic. “Some exercises last two and a half hours. But because they always change, it doesn’t feel like that”.

“Tuchel is not trying to reinvent football,” insisted the BVB sporting director Michael Zorc while the man himself professed modestly that he was only there to build on the “fantastic foundations” that Klopp had left behind. But the new training regime, coupled with a strict dietary regime (no more pasta from Dortmund’s best Italian restaurant at the training ground, only wholemeal products) and a stronger focus on possession football have already transformed beyond all recognition the unsettled, injury-ravaged team that had limped to seventh last season. Borussia have scored 116 goals this season, are unbeaten since the winter break and continue to breathe down Bayern’s necks, five points behind them, to turn the Bundesliga title race into the closest contest of all the big leagues.

“It’s a gift to coach this team,” Tuchel said after the 3-2 win over Werder Bremen on Saturday. The feeling is mutual. Important players such as the captain Mats Hummels, Marco Reus and Ilkay Gündogan, who all struggled in 2014-15, have refound their form as part of a functioning collective that can change tack and shift shape when Tuchel snaps his fingers on the touchline.

Dortmund were initially worried that the hardcore supporters might not warm to Klopp’s more introvert, far less vocal successor. At his last game at the Signal Iduna Park, the Swabian warned fans against making comparisons between himself and the new boss, for fear of “damaging the fantastic memories and hampering the fantastic future”. On Thursday night, however, the comparison might well turn out to be unflattering for the returning hero. If Tuchel can repeat the pattern he set at Mainz after succeeding and eventually bettering Klopp – who was in charge at Dortmund for seven years, just as he was at Mainz – at a second club, his reign at Westphalia promises some trophy haul, perhaps starting with a triumph in the Europa League. But Liverpool fans might one day enjoy Tuchel’s pioneering work too. “I’m so happy that Kloppo has finally made up his mind,” the Bavarian joked when Klopp’s Anfield appointment was announced in October. “Now I know where I’ll be going next as a coach.”