Borussia Dortmund fans return to their seats after a protest about ticket prices during the DFB Cup Quarter Final match between VfB Stuttgart and Borussia Dortmund at Mercedes-Benz Arena on February 9, 2016 in Stuttgart, Germany. (Photo by Alex Grimm/Bongarts/Getty Images)

Borussia Dortmund fans return to their seats after a protest about ticket prices during the DFB Cup Quarter Final match between VfB Stuttgart and Borussia Dortmund at Mercedes-Benz Arena on February 9, 2016 in Stuttgart, Germany. (Photo by Alex Grimm/Bongarts/Getty Images)

Borussia Dortmund progressed to the DFB-Pokal semi-finals on a night when their players temporarily became ball boys after disgruntled fans threw dozens of tennis balls onto the pitch in Stuttgart.

Dortmund supporters made their anger about the hosts' ticket prices known in the build-up Tuesday's cup tie, and that led to an unusual interruption midway through the first half.

Fans smuggled tennis balls into the Mercedes-Benz Arena and threw them onto the pitch, disrupting a match which Dortmund went on to win 3-1.

The incident happened after ticket prices also hit the headlines in England over the weekend, with an estimated 10,000 Liverpool supporters leaving Anfield after 77 minutes of Saturday's draw with Sunderland in protest of the club's new pricing structure for next season.

Dortmund took the lead in Stuttgart through Marco Reus' fifth-minute strike but the in-form home side - on a four-match Bundesliga winning streak - drew level in the 21st minute when Lukas Rupp levelled.

The game was then disrupted in the 24th minute when dozens of tennis balls were thrown onto the pitch near the corner of the stadium housing the visiting Dortmund fans.

The balls were cleared by players from both sides, after which last season's runners-up Dortmund would go on to secure victory with goals from Pierre-Emerick Aubameyang in the 31st minute and Henrikh Mkhitaryan in the 89th.

In Tuesday's early kick-off, Werder Bremen also secured a 3-1 away win, at Bayer Leverkusen.

Javier Hernandez's 22nd-minute penalty put Bayer ahead but Werder drew level through Santiago Garcia and then took a 42nd-minute lead through Claudio Pizarro's penalty after Borges Wendell had been sent off for the hosts.

Florian Grillitsch then wrapped by Werder's win with their third goal seven minutes from time.

Belfast Telegraph