* Striker Haaland nets double
* Teenager Reyna also on target (Updates with details)
BERLIN, Sept 19 (Reuters) - Borussia Dortmund's Erling Haaland scored twice and teenager Giovanni Reyna added another goal as they cruised past Borussia Moenchengladbach 3-0 in their season opener on Saturday.
The 20-year-old Haaland scored a 54th minute penalty, awarded for a foul on Reyna, and bagged another with a sensationally quick counter-attack and a Jadon Sancho assist as Dortmund utilised their fearsome youthful attacking weapons.
Norway forward Haaland, who joined in January, took his tally to 15 goals in his 16 Bundesliga games so far this year.
A day after Bayern Munich opened their season with an 8-0 demolition of Schalke 04, Dortmund sent a warning to the title holders with their dominant performance over Gladbach, who will be competing in the Champions League this season.
Reyna opened the scoring in the 35th minute after combining perfectly with fellow 17-year-old Jude Bellingham, making his league debut after joining from Birmingham City.
Reyna's first league goal made him the second youngest American to score in the Bundesliga after former Dortmund winger Christian Pulisic, who is now at Chelsea.
Gladbach had a good early chance through Jonas Hofmann but struggled throughout with Dortmund's speed, and not even the introduction of strikers Alassane Plea and Marcus Thuram could turn things around.
The hosts, playing in front of a crowd limited to 9,300 fans in their 80,000-capacity stadium due to COVID-19 restrictions, also hit the crossbar with a Sancho header. (Reporting by Karolos Grohmann; editing by Ian Chadband and Ken Ferris)