Brace yourselves, Bundesliga fans, for a special Sunday service involving the division's top four teams that is set to be so pulsating, it should come with a health warning.

With league leaders Union Berlin hosting Borussia Dortmund and second-placed Freiburg visiting reigning champions Bayern Munich, there is nothing else for it but to cancel the rest of your Sunday plans and place the Bundesliga at the very top of your agendas.

Once the tantalising Cologne versus Augsburg curtain raiser has drawn to a close, it's time to tune in to see Union, the side that has caught the imagination of the footballing world, as they host a Dortmund team still giddy after that late, late equaliser against Bayern in Der Klassiker. An appealing prospect  between Urs Fischer's charges and Edin Terzic's BVB whose outcome is impossible to predict, what can definitely be guaranteed at the Stadion An der Alten Försterei this weekend is eye-catching drama.

Watch: Klassiker cracker's amazing finish  

Union opened a two-point lead at the top of the standings following a 1-0 win against Stuttgart last time out, a result that extended the Berliners' best-ever start in the top flight. Indeed, Die Eisernen's 20-point haul after the opening nine Bundesliga game is worthy of even more praise when you consider Sunday's hosts never even managed such a return during their time in the second division. What's more, the Köpenicker high flyers have the meanest defence in the Bundesliga having conceded just six times so far. Ahead of the the visit of fourth-placed Dortmund, many are beginning to wonder where all of this might end for The Irons.

"Dreaming is allowed. Why not? Anything is possible in football as the past has shown," Germany legend Michael Ballack recently told Sportbild when asked about Union's prospects. Ballack was famously part of the promoted Kaiserslautern team that shocked a nation by winning the 1997/98 Bundesliga title and the ex-Bayern and Bayer Leverkusen midfielder is a big admirer of what Union have been doing lately.

Watch: Leaders Union victorious at Stuttgart 

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"I like the way they play football," Ballack said. "It's a nice mix in terms of good play, physicality and winning individual duels. The team also has a good mentality; the fans identify with that," the former Germany international added.

Dortmund will arrive in the German capital having been well schooled on one of the Bundesliga's most in-form attacking partnerships. Sheraldo Becker (six goals, three assists) and USMNT international Jordan (three goals, two assists) will take some stopping, especially given that the pair have accounted for seven of Union's eight goals at home this season. However, in Youssoufa Moukoko and Anthony Modeste, Sunday's visitors have a Klassiker-cracking duo that might be too tempting a starting prospect for BVB tactician Terzic to ignore.

Watch: Deadly duo Jordan and Becker

Moukoko's debut Bundesliga goal came against Union back in December 2020 when, at 16 years and 28 days, he became the German top flight's youngest scorer. After being assisted by teammate Modeste last weekend, the teen netted as a starter for only the second time to help his side back into a game against Bayern which they had been trailing by 2-0.

Substitute Modeste - who only had the ball four times in the match - then scored an equaliser that Borussia fans are still watching to this day. "I'm delighted for him," Moukoko said of Modeste. "I learn a lot from him; he's like a father to me. We'll see many more goals from him," the talented teen continued.

Midfielder Jude Bellingham, who has excelled in the Dortmund engine room this season, pointed to Die Schwarzgelben's "character" and "quality" as some of the reasons behind the spectacular comeback, the England midfielder adding that, "The late equaliser felt very special; it was a complete performance from the entire team."

Looking ahead to Sunday, Dortmund have won their last three Bundesliga games against Union and even inflicted the Berliners' last reverse at their Alte Försterei home back in February. Die Eisernen have been unbeaten in their own backyard in the 10 matches since then, however, meaning the league leaders will take some beating.

Watch: Union are shaking up the Bundesliga

As will Freiburg, who are set to face the mighty Bayern for a 45th time in the Bundesliga on Super Sunday. Christian Streich's men were top of the pile after Matchday 5 for only the second time in the club's history and they travel to the Allianz Arena boasting a seven-game unbeaten streak, currently the longest run of any team in the top division.

The challenge next facing Freiburg - who were held to a 2-2 draw at Hertha Berlin last week - is to attempt to gain a very first victory away to Julian Nagelsmann's side, who are 19 and three at home against the boys from the Black Forest.

What will lift last season's losing DFB Cup finalists' hopes of causing an upset in Bavaria is the fact that third-placed Bayern are enduring their worst start to a season for 12 years. The last time Sunday's hosts had 16 points after nine matches at the beginning of a campaign was back in 2010/11, when Dortmund went on to win the title.

Watch: The Freiburg feel-good factor 

Those at Freiburg might flinch at any mention they could be in the frame for Bundesliga glory this term, but heading to Munich as one of only two unbeaten teams away in the Bundesliga so far in 2022/23 (Werder Bremen are the other) only raises the chatter outside the Breisgau club.

The team's top scorer with four Bundesliga goals, Michael Gregoritsch, recently described Freiburg as, "A super beautiful city, a super cool club" and "a team with great character, which is why I feel very much at home here." When pressed on what it is exactly that Streich's side are getting right this term, the former Augsburg striker told Sportschau, "We only go onto the pitch with one hundred percent commitment and passion.

"Everyone here knows that every game is do or die," the Austrian added. "After that, it's also possible for us to play [good] football against opponents. The basics are right for every game," Gregoritsch continued. "What sets us apart is that we have unbelievable quality when it comes to adapting to the games again and again."

Watch: Sadio Mane vs. Michael Gregoritsch

And adapt Freiburg will have to do once more against Sadio Mane, Jamal Musiala and Co. For many observers, Bayern - the Bundesliga's top scorers with 25 goals - are due a resurgence after posting just one win in six in the Bundesliga.

Whether Nagelsmann's crew can set sail once again on what is set to be a spectacular Sunday's entertainment will be one of the many fascinating facets that keep us all on the edge of our seats. So join us on bundesliga.com and across our social media channels to find out just who will be flying the flag at the top of the pile come Matchday 10's denouement.

About the clubs

SC Freiburg

Europa-Park Stadion

Borussia Dortmund

SIGNAL IDUNA PARK

FC Bayern München

Allianz Arena

1. FC Union Berlin

An der Alten Försterei