Bayern's fight to keep their title from Dortmund and the Bundesliga's Leicester

The Bundesliga title race is as tight as it has been for over a decade and this Sunday serves up a huge game at the top of the table, live on Sky Sports.

Heading into the weekend, Bayern Munich, Borussia Dortmund and unlikely contenders Union Berlin were all level on 43 points after 21 games in the German top flight. This is the latest there has been a three-way tie at the top since the introduction of three points per win in 1995/96.

Dortmund, the last side to break Bayern's vice-like grip on the title under Jurgen Klopp in 2012, beat Hoffenheim 1-0 on Saturday afternoon to see them take a three-point lead at the top of the table, but their two title rivals are hot on their heels.

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Bayern, Germany's perennial champions, host underdogs Union Berlin at the Allianz Arena on Sunday, live on Sky Sports; kick-off 4.30pm.

Here, we take a look at the three teams battling it out at the top of the Bundesliga ahead of a pivotal weekend with the help of Sky Germany reporter Uli Kohler...

Bayern Munich

It's nearly March and still Bayern don't have a commanding lead at the top of the Bundesliga. So what's going on at Germany's most dominant club?

Head coach Julian Nagelsmann has managed to win just two of his last six games in the league, most recently losing to Borussia Monchengladbach 3-2 last Saturday after seeing Dayot Upamecano sent off after eight minutes.

Nagelsmann appeared to be feeling the pressure after the game as he lost his temper with official Tobias Welz publicly, shouting his discontent before going into the referee's room in plain sight of the press.

The 35-year-old later apologised on Twitter: "Emotions are part of sport. And given the red card, I had to vent after the game.

"However, I have to apologise for the choice of words to the team around Tobias Welz. Unfortunately I went too far there."

Bayern were in ripe form before the World Cup but have failed to hit their stride again, losing almost as many points (9) in the six league matches back as they had in the previous 15 games (11).

This is the German champions' lowest number of wins at this stage of the season since 2010/11, when Dortmund won the Bundesliga title. Nagelsmann doesn't want a repeat of that. Louis van Gaal, Bayern's head coach at the time, was sacked in April 2011 before the season was over.

Sunday's game against Union has taken on huge significance in Munich as Nagelsmann heads into a pivotal period of the season, which includes the second leg of Bayern's Champions League last-16 tie against Paris Saint-Germain.

Drop points on Sunday and Nagelsmann could really be under pressure.

Union Berlin

Union Berlin are the team that no one expected to be here. Promoted to the Bundesliga for the first time in the club's history in 2019, this is somewhat of a fairytale story.

But it's no accident, either. Union showed everyone just how good they are last season, clinching fifth spot in the league.

Urs Fischer, the Swiss coach in charge of Union, has worked wonders on a relatively shoestring budget to compete with Bayern and Dortmund so far into the season.

Union, who have spent around £21m on signings this season, broke their transfer record in January in a deal with Celtic for right-back Josip Juranovic worth an initial £7.5m.

Bayern, for comparison, broke their transfer record in 2019 as they purchased Lucas Hernandez from Atletico Madrid for more than £70m and have spent around £128m on signings this season.

Union head coach Fischer has created the best defence in the division behind only Bayern to give his side a solid base from which to launch a potential title challenge. They've allowed just 24 goals this season compared to Bayern's 21 conceded.

One of their biggest strengths has been their home form. Union are unbeaten at the Stadion An der Alten Forsterei in the Bundesliga this season, a run which has seen them draw with Bayern at their peak and beat Dortmund.

Union have been less convincing on the road, but have experienced an up-tick in form post-World Cup like Dortmund and won all three of their away league games, making Sunday's trip to the Allianz a good litmus test of their title credentials.

Borussia Dortmund

Dortmund have taken full advantage of Bayern's stuttering return to action following the World Cup by winning all eight of their league matches.

Edin Terzic's side are the form team in Germany and as expected on Saturday, won 1-0 at Hoffenheim, who are now on a five-game losing run and have not won since beating Schalke 3-0 in October.

Dortmund have now beaten all 10 of the teams they have faced since the season's restart - including Chelsea in the Champions League - making them real contenders to push Bayern all the way.

Julian Brandt, the Germany midfielder, has been a revelation for Dortmund in this period. The midfielder, delivering when it counts for the German club, netted the winner against Hoffenheim on Saturday, scoring for the fourth successive league game and the ninth time in total this season.

Karim Adeyemi, the 21-year-old striker signed from Red Bull Salzburg in the summer, has been another of Dortmund's star performers, netting in their last four games prior to Saturday. However, he is now out with a hamstring injury suffered while setting up Dortmund's second goal in a 4-1 win over Hertha Berlin.

With Adeyemi and Youssoufa Moukoko now unavailable due to injury, it will be a test of Dortmund's other options, including English teenage duo Jude Bellingham and Jamie Bynoe-Gittens, to see if they can step up.

Watch Bayern Munich vs Union Berlin on Sunday from 4.20pm, live on Sky Sports Action; kick-off 4.30pm.