On January 19, 2005, he won the Dutch Muay Thai title at 86 kg when he knocked out Bas van den Muijsenberg in Tilburg.

After knocking out local fighter Mario Ostos in the quarter-finals and Cameroon's Eric Kouman in the semis, he was defeated by Henriques Zowa via unanimous decision in the final.

He KO'd Johan Mparpagiannis in the first round at the K-1 World MAX North European Qualification 2007 in Stockholm on November 27, and took revenge on Naoufal Benazzouz by TKOing him in Roosendaal, Netherlands on December 9.

He defeated Wallis in the Netherlands on April 7, and then entered the eight-man tournament at K-1 Fighting Network Romania 2007 on May 4 to make his K-1 debut.

[4] After stopping an aging Rene Rooze at the It's Showtime 75MAX Trophy 2008 on March 15, Zimmerman advanced to the final eight of the Europe GP at the K-1 World Grand Prix 2008 in Amsterdam on April 26.

Advancing to the final against Zabit Samedov, he took a majority decision win after a hard-fought three rounds to become the K-1 European Champion and qualify for 2008 K-1 World Grand Prix.

Bouzidi was given the win when referee Joop Ubeda stopped the bout due to a cut on Zimmerman's knee in the first round.

[9] On April 3, Zimmerman faced Golden Glory teammate Semmy Schilt for the K-1 Super Heavyweight Championship at the K-1 World Grand Prix 2010 in Yokohama.

[10] He returned to the winning column on May 21, taking only twenty-four seconds to demolish Romanian fans' favourite Cătălin Moroşanu at the K-1 World Grand Prix 2010 in Bucharest.

[12] In a superfight at the K-1 World Grand Prix 2010 Final in Tokyo, Japan on December 11, he dropped a unanimous decision (30–28, 29–28, and 30–28) to Ewerton Teixeira to bring his tally for the year to 1–3.

On March 19, he demolished Zinedine Hameur-Lain in just over thirty seconds in a superfight at the United Glory 13: 2010-2011 World Series Semifinals in Charleroi, Belgium.

He totally overwhelmed the Frenchman with kicks and punches, breaking Hameur-Lain's left arm in the process, and forced the referee to stop the fight.

[14] Then, in another superfight at the United Glory 14: 2010-2011 World Series Finals on May 28 in Moscow, Russia, he avenged his 2009 loss to Mourad Bouzidi by taking a unanimous decision over him.

[15] Continuing his run of form, he knocked out Nikolaj Falin inside the first fifteen seconds of the first round of their contest in Merseburg, Germany on August 28.

[17] Instead, Zimmerman took part in a one-night, eight-man tournament in Oradea, Romania at the SuperKombat: Fight Club event on November 17.

In the quarter-finals, he knocked Sebastian van Thielen cold with a right hook before stopping German veteran Stefan Leko in the semis by referee stoppage.

Zimmerman did have his moments, where he rocked his opponent multiple times, but his lack of mobility and head movement made him an easy target for the much taller Schilt.

Time ran out just as he was making a comeback, however, and, due to the tournament's "best of three" format, he lost a unanimous decision after two, two-minute rounds.

[30] He stopped Edwards in round one, scoring two knockdowns over the Australian, before giving an almost identical performance in the final against Anderson "Braddock" Silva as he knocked his Brazilian opponent down three times to win via another first-round TKO and take the tournament crown.

[32] Zimmerman completed a trilogy of fights against Rico Verhoeven when he faced him on February 6, 2015, in the main event at Glory 19: Virginia.

[33] The anticipated bout ended in anticlimactic fashion as Zimmerman sustained a knee injury in the second round, allowing Verhoeven to retain his Heavyweight title.

[43] Zimmerman lost the fight by knockout in round 2, failing to beat the ten count after being knocked down by a spinning heel kick.

[46] His sophomore bout in the sport came almost fifteen years removed from the debut, against Tomasz Sarara at KSW 81: Bartosiński vs. Szczepaniak on April 22, 2023.