By Jake Donovan

Wladimir Klitschko looks to extend his lengthy heavyweight championship reign, as he faces top contender Kubrat Pulev this Saturday at the O2 World Arena in Hamburg, Germany.

Veteran Tony Weeks has been tasked with keeping things in order for the heavyweight title fight, which airs live in the United States on HBO (Saturday, 4:45 p.m. ET).

Klitschko (62-3, 52KOs) has held at least one major belt since April '06, good for the second longest title reign in boxing history. He has served as World lineal champion since June '09, when he stopped then-unbeaten Ruslan Chagaev in nine rounds to fill the void left behind for more than five years following Lennox Lewis' announced retirement in 2004.

Overall, Klitschko has racked up 16 consecutive alphabet title defenses and nine lineal championship defenses. His most recent win came in April, stopping Alex Leapai in five rounds.

Pulev (20-0, 11KOs) enters his first career title fight. The opportunity should have come much sooner, but the unbeaten Bulgarian had a hard time convincing his divisional peers to step in the ring with him. Tomasz Adamek and Tyson Fury both declined what would have been final title eliminators, leaving Pulev out of the ring for 11 months before defeating Tony Thompson last August to become Klitschko's mandatory title challenger.

His time since then has been spent in stay busy bouts, scoring early knockouts over subpar competition while awaiting his title opportunity.

The bout was originally due to take place in September, but postponed due to Klitschko suffering an injury during training camp.

Officials were also named by the World Boxing Organization (WBO) for its junior flyweight title fight in Cebu, Philippines.

Donnie Nietes (33-1-4, 19KOs) makes the fifth defense of his alphabet belt as he faces unbeaten Carlos Velarde (20-0, 11KOs)

The referee for this fight will be Samuel Viruet, from United States. The judges will be Rose M. Lacend, from United States, Salven Lagumbay, from Philippines, and Masakazu Murase, from Japan.

Jake Donovan is the Managing Editor of Boxingscene.com, as well as the Records Keeper for the Transnational Boxing Ratings Board and a member of Boxing Writers Association of America . Twitter: @JakeNDaBox