Erling Braut Haaland continues his stunning Bundesliga start with two goals as Borussia Dortmund thrash Union Berlin

Norwegian 19-year-old makes it seven goals in three games, while Lewandowski grabs his 22nd of the season in Bayern Munich's win at Mainz

Borussia Dortmund's Erling Haaland celebrates after scoring his first goal against Union Berlin on Saturday. EPA

Dortmund's Erling Haaland is fouled by Union Berlin goalkeeper Rafal Gikiewicz earning his side a penalty. AP

Borussia Dortmund's Erling Haaland celebrates after scoring his first goal against Union Berlin on Saturday. EPA

Dortmund's Jadon Sancho, centre, celebrates with teammates after opening the scoring. EPA

Dortmund's Marco Reus scores their third gpoal from the spot. EPA

Dortmund's Erling Haaland scores his first. EPA

Erling Haaland and Dortmund manager Lucien Favre. EPA

Dortmund's Axel Witsel celebrates after scoring his side's fourth. AP

Union Berlin's 's Christopher Trimmel battles with Jadon Sancho of Dortmund. EPA

Erling Haaland scores his team's second goal. Getty

Robert Lewandowski heads home Bayern Munich's first goal against Mainz. Getty

Robert Lewandowski, left, celebrates his goal for Bayern. AP

Bayern Munich's Thomas Muller celebrates after scoring the second goal. AFP

Thiago Alcantara scores Bayern Munich's third goal. Getty

Thiago Alcantara celebrates after scoring. Getty

Mainz defender Jeremiah St Juste and Bayern's Robert Lewandowski battle for possession. AFP

Erling Braut Haaland made it seven goals in three games for Borussia Dortmund after scoring a double in Saturday's 5-0 Bundesliga thrashing of Union Berlin while Bayern Munich went top of the table.

The 19-year-old Haaland, who had netted five times in his first two appearances since signing from Salzburg, scored either side of half-time at Signal Iduna Park after being handed his first Dortmund start by coach Lucien Favre.

Haaland's tally is the most by any Bundesliga player in their first three league matches.

Dortmund moved to third in the table, three points behind leaders Bayern Munich, who beat Mainz 3-1.

RB Leipzig can regain top spot if they beat fourth-placed Borussia Moenchengladbach at home in the late game.

In Dortmund, 19-year-old England winger Jadon Sancho became the first teenager to score 25 goals in the Bundesliga when he started the rout with a looping shot past Union goalkeeper Rafal Gikiewicz.

Haaland then added to his record run on 18 minutes when he was presented with a simple tap-in from a Julian Brandt cross.

The hosts were dominating as Haaland won a penalty, which captain Marco Reus converted mid-way through the second half.

Central midfielder Axel Witsel made it 4-0 on 70 minutes, firing home after Sancho's brilliant pass took out two defenders and set up his Belgian team-mate.

Haaland completed the rout when a Brandt back-heel fell into his path and he drilled his shot past the despairing Gikiewicz.

n Mainz, goals by Robert Lewandowski, Thomas Mueller and Thiago Alcantara sealed Bayern's away win to go two points clear.

Bayern wasted no time taking the lead despite the sodden conditions as the Bundesliga's top scorer Lewandowski netted his 22nd league goal after just eight minutes to herald a powerful first-half by the defending champions.

Mueller hit their second on 14 minutes, finishing a move he started after Lewandowski and Leon Goretzka shredded Mainz's defence.

Alcantara made it 3-0 on 30 minutes by beating three defenders with superb footwork before smashing his shot past Mainz goalkeeper Robin Zentner.

Goretzka played an unlucky part in the Mainz goal when a header by defender Jeremiah St Juste cannoned off the back of his head and beat Bayern goalkeeper Manuel Neuer on the stroke of half-time.

Fifth-placed Leverkusen lost ground in the table when they went down 2-1 at Hoffenheim thanks to goals from striker Andrej Kramaric and Danish defender Robert Skov.

A Timothy Chandler header just before the whistle rescued a point for Eintracht Frankfurt in their 1-1 draw at Fortuna Duesseldorf, who moved off the bottom.

It was Fortuna's first game under new coach Uwe Roesler, who took charge on Wednesday in a bid to avoid relegation.

Augsburg went ninth after they came from behind to beat Werder Bremen 2-1 with goals by Florian Niederlechner and Ruben Vargas after their defender Tin Jedvaj had scored an early own goal.