Lukasz Kubot and Marcelo Melo take the doubles title in Halle.

Roger Federer celebrates his ninth Gerry Weber Open title in Halle.

Roger Federer tries to win his ninth title at the Gerry Weber Open in Halle.

Roger Federer takes on Alexander Zverev in the Gerry Weber Open final.

Alexander and Mischa Zverev are one win away from a doubles title on home soil.

Alexander Zverev will try to win his first grass-court title on Sunday in Halle.

Roger Federer battles past #NextGenATP Karen Khachanov in the Halle semi-finals on Saturday.

Alexander Zverev is through to another semi-final in Halle.

Roger Federer is two matches away from a ninth title in Halle.

Marcelo Melo (back left) leaps into the Halle doubles final with Lukasz Kubot.

Karen Khachanov beats Andrey Rublev to reach his first semi-final of the season.

Roger Federer is through to his 15th quarter-final in Halle.

Florian Mayer dives into the Halle quarter-finals on Thursday.

Defending champion Florian Mayer extends his winning streak in Halle.

Lukasz Kubot and Marcelo Melo break Fernando Verdasco to love en route to winning the first nine points of the match.

Alexander Zverev hasn't dropped serve in reaching the Halle quarter-finals.

Alexander Zverev receives a trophy commemorating his break into the Top 10 of the Emirates ATP Rankings earlier this year.

Roger Federer rolls during his opener at the Gerry Weber Open in Halle on Tuesday.

Tommy Haas says farewell to Gerry Weber Open fans with daughter Valentina in his arms.

Kei Nishikori goes airborne to beat Fernando Verdasco on Tuesday in Halle.

Dominic Thiem looks to improve upon his semi-final run last year at the Gerry Weber Open in Halle.

Mischa Zverev, left, and Alexander Zverev will meet Brian Baker and Alexander Peya in the second round of the Gerry Weber Open in Halle.

Frenchman Richard Gasquet breaks Gael Monfils three times to advance on Monday in Halle.

#NextGenATP star Andrey Rublev defeats 8th-seeded Albert Ramos Vinolas to move on to the second round of the Gerry Weber Open.

The expansive site of the Gerry Weber Open, which includes Gerry Weber Stadion and its retractable roof, which was added in 1994.

Lukasz Kubot (L) and Marcelo Melo win their fourth ATP World Tour doubles title of 2017 in Halle.