“We’re calling it the Jahrhundertspiel,” Kai Brünker says over the phone from Saarbrücken. “The game of the century. A big game, a derby, and it’s in a cup semi‑final. Everybody is speaking about it. You go to the bakery, people are speaking about it. You go into the city, you go for a walk, and people are saying: ‘You have to win against ’Slautern!’”
For the Saarbrücken coach, Rüdiger Ziehl, the reminder that this is no ordinary week comes with the constant pinging of his phone from friends and casual acquaintances pestering him for a ticket. On Tuesday night the third-division side from the very west of Germany, pinned right up against the French border, will write the next chapter in one of the most remarkable stories anywhere in European football this season.

The continent rejoiced in unison when Saarbrücken knocked out Bayern Munich in the second round of the DFB-Pokal in November. But pretty much nobody expected what happened next: a 2-0 win over Eintracht Frankfurt in the last 16, before Borussia Mönchengladbach were beaten by a 93rd-minute winner from Brünker this month.

Now comes a semi-final against their bitter local rivals Kaiserslautern. In May, one of them will become the first non-Bundesliga team to reach the cup final since 2011. Saarbrücken, for their part, would become the first third-tier team to get there since unfancied Union Berlin made the final in their home city in 2001.

“You can’t explain it,” Ziehl says of a fairytale run that began all the way back in August with a 2-1 win over second-tier Karlsruhe. “To this moment, nobody can believe it. Bayern Munich, then Frankfurt, then Gladbach? Normally you don’t have a chance.”

Saarbrücken’s home stadium holds only 16,000 fans, but what it lacks in numbers it makes up in hostility. “Real hell is blue and black,” the fans like to say, and in a competition where the lowest-ranked clubs are automatically granted home advantage, the fiery atmosphere at the Ludwigsparkstadion has become a kind of protagonist in its own right.

“It’s a big part of this story,” Ziehl says. “You feel it when you come to the stadium. More than a normal league game. The stadium is full one and a half hours before. When you warm up, it’s a totally different atmosphere. During the game, every duel you win, every good action, they’re celebrating.”

That Saarbrücken have been able to reproduce their white-hot cup form only fleetingly in the Dritte Liga, where they are 10th and well out of the promotion race, is less surprising when you look at their squad: a mixture of youngsters who never quite made it at the top level and experienced journeymen such as the centre-forward Brünker, who in England is perhaps best known for a one-year spell at Bradford City that can charitably be described as mixed.

“It was a really intense time,” Brünker says of a spell that produced 31 appearances and a single goal, against Oldham in the Checkatrade Trophy. “In a football sense, I wasn’t the scoring machine that Bradford hoped I would be. But I had a really nice time and I had this feeling of connection to the Bradford fans. I just wanted to give 100% for them.”

He still watches all their games and after the tape is turned off spends several minutes singing the praises of Andy Cook, who he hopes can fire them to League Two promotion this season.

But it took Saarbrücken, and the careful tutelage of Ziehl, to get him back on target and rebuild his confidence. “He trusts me,” says Brünker. “You have to get that trust from the manager. Even when the ball is not rolling for you, you can make it better with your mentality. When you defend well, when you stay compact, when you close the room for the opponent.”

The 29-year-old plays at the vanguard of a hardworking 3-4-3, with the emphasis – at least against bigger teams – on closing down space and springing counterattacks. Asked to define his coaching philosophy, Ziehl prefers to express it in terms of values. “That you are a team on the pitch,” he says. “That the defence wants to have the ball, not just fight. That the strikers also have to defend.”

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And though it is more than three decades since Saarbrücken breathed the thin air of the Bundesliga, this is a proud footballing region with a rich heritage. The Saarland even had its own international team in the 1950s, as France tried and failed to prevent the region from being absorbed back into Germany after the second world war.

“It’s not a huge city but we have many, many fans,” Ziehl says. “And with these games against the big clubs in Germany, we have a new feeling in the city again, like what the feeling was years ago. You feel you’re part of the ‘big football’.”

It is the first time in the history of the DFB-Pokal that only one Bundesliga team has made it to the semi-finals. (Xabi Alonso’s Bayer Leverkusen face Fortuna Düsseldorf in Wednesday’s second semi-final.) And given the debates swirling around European football about competitive balance and the growing gap between the richest and the poorest, this year’s competition feels like its own quiet act of rebellion: a reminder that however stacked the odds, however unlevel the playing field, there are still fleeting moments when true sporting ingenuity finds a way.

“The gap is big, and getting bigger,” says Ziehl. “But the Pokal in its history has shown that teams from the second or third league can win. David against Goliath. And when you’re so close to the final, you think about it for sure. It’s so close. Everybody’s dreaming.”