* Robben and Mueller win Cup for Bayern
* Secure domestic double after Bundesliga triumph (Updates with more details, quotes)
BERLIN, May 17 (Reuters) - Bayern Munich restored their undisputed dominance in Germany when they beat rivals Borussia Dortmund 2-0 with two extra-time goals on Saturday to win the German Cup and secure their tenth domestic double.
Dutchman Arjen Robben, who scored the winner against Dortmund in the Champions League final last season, tapped in at the far post in the 107th minute after the country's top two teams slugged it out in a goalless but entertaining 90 minutes.
Thomas Mueller then raced clear deep in stoppage time to complete the win over their bitter rivals immediately after Marco Reus had missed a chance to equalise.
Victory ended a bad run for Bayern who had won the league title with seven games to spare in Pep Guardiola's first season in charge before hitting a slump in form, including a comprehensive Champions League semi-final defeat by Real Madrid.
"When a team wins the league title then it is already a good season," Guardiola told reporters. "But we are happy to have achieved it today. It was a big title."
For scorer Robben the win marked the end of a successful season.
"It was a very important goal," Robben said. "This was a Cup, and we really wanted to win it. We are here, won the double, had a super season and that's the bottom line."
Saturday's final was marked by a controversial goalline incident with Mats Hummels' header in the 64th minute cleared on the line by Bayern defender Dante with television replays showing the entire ball may have crossed the line.
German football bosses earlier in the year voted against the introduction of goalline technology but the latest incident is set to renew the debate.
For Dortmund, the defeat completed a season without silverware, with top striker Robert Lewandowski failing to score in his last game before joining Bayern next season.
"It was big title, a final and we had our chances. They (Bayern) wanted to lure us out and then counter attack," Dortmund manager Juergen Klopp told reporters.
"We also wanted to play a bit differently. But we did not defend very well. It did not work out and we have to accept it. I am sorry."
Bayern, missing injured Bastian Schweinsteiger and David Alaba, also had captain Philipp Lahm limp off with a muscle injury after less than half an hour.
Already missing Thiago Alcantara, who had knee surgery on Thursday, Bayern were desperate to end the season on a high after their form nose-dived spectacularly in March.
Guardiola set up his team with a three-man backline in a 3-5-2 formation and an additional player in midfield as both teams pressed high from the start.
There were few chances in the first half with both sides cautious not to be caught out by a quick break.
Dortmund, who beat Bayern 3-0 in the league last month, thought they had scored when Hummels headed towards goal with Dante, standing inside the goal, clearing near the line, but referee Florian Meyer waved play on.
Oliver Kirch then tested Bayern keeper Manuel Neuer with a long-range effort and Robben responded with a shot of his own as the game went into extra-time.
The Dutchman then beat keeper Roman Weidenfeller, who had repeatedly denied the winger, from a Jerome Boateng pass.
Mueller sealed their win after a fine pass from substitute Claudio Pizarro. (Reporting by Karolos Grohmann; editing by Justin Palmer and Josh Reich)