Dortmund's Erling Haaland celebrates after scoring his third goal of the game during their German Bundesliga match against FC Augsburg at the WWK Arena in Augsburg, Germany on Saturday. Photo: Tom Weller/AP

BERLIN – New signing Erling Braut Haaland climbed off the bench, scored with his first attempt and then grabbed a hat-trick as Borussia Dortmund fought back to win 5-3 at Augsburg in a Bundesliga thriller on Saturday.

Leaders RB Leipzig also came from behind to beat Union Berlin 3-1 at home in the late game, meaning fourth-placed Dortmund remain seven points behind after 18 games.

The Black and Yellows returned from their mid-season break with a performance to both annoy and thrill their fans, with substitute Haaland netting three in just 20 minutes as they rallied from 3-1 down.

"It was a good debut, I'm happy," an understated Haaland told Sky in an ice-cool interview.

In other games, Cologne triumphed 3-1 over Wolfsburg, Eintracht Frankfurt won 2-1 at Hoffenheim and Freiburg beat Mainz 2-1 away. Werder Bremen sealed a key 1-0 win at dropzone rivals Fortuna Dusseldorf, leapfrogging the hosts into the relegation play-off spot.

Champions Bayern Munich, third and level on points with Dortmund, visit Hertha Berlin on Sunday when bottom side Paderborn host Bayer Leverkusen. Schalke beat second-placed Borussia Moenchengladbach 2-0 on Friday with Gladbach now five points adrift of Leipzig.

Dortmund coach Lucien Favre decided not to start with Norwegian Haaland, 19, despite the new arrival from Salzburg being widely acclaimed as the most exciting young striker in Europe.

It was even more of a surprise as fellow forward Paco Alcacer missed out on a squad berth altogether, although club officials have said any transfer speculation surrounding the Spaniard is just rumours.

The absence of an out-and-out striker for Dortmund was laid bare by Marco Reus missing a golden chance on eight minutes when he somehow scooped a routine finish wide.

Augsburg's Florian Niederlechner was offside as the home team had a goal chalked off, but he soon made amends when he slid in to score on 34 minutes after excellent work by Ruben Vargas following a Dortmund mistake.

There was no sign of Haaland for the start of the second half and quickly it was 2-0 thanks to Marco Richter's booming effort.

Julian Brandt soon pulled one back for Dortmund with a neat turn-and-finish in the box but Niederlechner made it 3-1 on 55 minutes.

Haaland then immediately entered the fray and scored with his very first Bundesliga chance, a fine goalpoacher's finish.

Just two minutes later and it was 3-3 with Jadon Sancho running on to a long ball to score, as mid-table Augsburg fell apart.

Haaland then netted again from close range on 70 minutes but a flag was raised for offside in the build-up. The video assistant though ruled the goal to be legal.

The 20 million-euro (22 million dollar) signing, who also scored a hat-trick on his Champions League debut for Salzburg in September, then completed a dream treble 11 minutes from time.

He becomes the second player to score a Bundesliga hat-trick for Dortmund on his debut, following Pierre-Emerick Aubameyang in 2013 - also against Augsburg.

"He got straight into the game, showed his strength, ran the channels and scored three goals," Favre said, adding that the Norway forward had not started because he did not feel the teenager was fully fit.

"He gives us something different. It was a crazy game."

Leipzig went behind after just 10 minutes when they sloppily gave the ball away in midfield and allowed Union to charge forward, Marius Buelter calmly netting for the promoted team.

Union fans protested against Leipzig's roots and Red Bull sponsor but were silenced early in the second half by a thumping Timo Werner strike from the edge of the box.

Shortly afterwards Marcel Sabitzer hooked in following a corner to complete the Leipzig turnaround.

Werner then added some gloss with another fine finish seven minutes from time, taking over from Bayern's Robert Lewandowski at the top of the Bundesliga scoring charts with 20.