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

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

Alexander Zverev battles in the Gerry Weber Open final in Halle for the second year in a row.

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.

Just about everyone is a fan of Roger Federer in Halle.

Karen Khachanov held a set point in the second set, but couldn't topple Roger Federer.

Roger Federer is through to his 11th final in Halle.

Roger Federer reaches his 11th Halle final on Saturday at the Gerry Weber Open.

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

Alexander Zverev survives a marathon battle against Roberto Bautista Agut to reach the Halle semi-finals.

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.

Roger Federer remains in pursuit of a ninth title in Halle.

#NextGenATP player Karen Khachanov is through to his first grass-court quarterfinal.

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

Defending champion Florian Mayer extends his winning streak in Halle.

Chase that! Dominic Thiem lobs Robin Haase Wednesday in Halle.

Dominic Thiem produces a deft drop volley Wednesday in Halle.

Robin Haase upsets second seed Dominic Thiem Wednesday in Halle.

Dominic Thiem, Philipp Kohlschreiber, Tournament Director Ralf Weber and his wife Irina, Roger Federer and Boris Becker enjoy the players' party Tuesday night at the Gerry Weber Open.

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.

Tommy Haas falls to Bernard Tomic in his last professional grass-court match on German soil.

Fernando Verdasco is defeated by Kei Nishikori in the first round of the Gerry Weber Open.

Mischa Zverev defeats qualifier Lukas Lacko to reach the second round of the Gerry Weber Open.

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.

Fans meet Philipp Kohlschreiber at the Daylong booth at the Gerry Weber Open.

Gael Monfils is defeated by Richard Gasquet on Monday 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.

The Zverev brothers celebrate their doubles victory over Philipp Petzschner and Florian Mayer on Monday in Halle.

Wild card Dustin Brown advances to the second round of the Gerry Weber Open after defeating Qualifier Vasek Pospisil.

Dustin Brown gets airborne in his match against Vasek Pospisil on Monday in Halle 2017.

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.

Albert Ramos-Vinolas falls to #NextGenATP player Andrey Rublev in the first round of the Gerry Weber Open in Halle.

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.

Australian Bernard Tomic defeats Tommy Haas on Tuesday in Halle.